They're more small explosive drones than actual rockets or artillery according to the background, kind of similar to the Hive Guard's projectiles.
Like little remote controlled bombs that have the controller on board.

Sure there's a FPS which has you steering the rockets just after you've fired them, there's also Batman Arkham: City's remote batterangs.

I can see things like KFF and Venomthropes becoming a huge problem.

So long as there's no doors blocking the way, ie. a clear path can be traced to the target, I don't see a problem. They're guided missiles... it's stretching a point a bit to think they can navigate along corridors, but a lot of 40K is "stretching the point". As you say, the rules are clear.

If an opponent really objected, I'd be happy to measure the range along the corridors to the target (instead of in a straight line) because, of course, that's the path the missiles would be taking; but in principle SMS in ZM is no more unfair than, say... Terminators. There's enough units in our army that aren't very effective, without ruling out the ones that are...

Yeah, I wondered about a KFF while sketching out a few possible Ork lists. But then I thought: it's a cover-rich environment. Is it really worthwhile spending points on getting a cover save? Maybe... but maybe not.

That's actually one of the things I'd expect to be included in the next set (which is presumably the Prison planet IA) as when things are that confined already, it's tricky to add more cover without making it almost unplayable due to space issues - pretty sure that in Anphelion Base they solved this by having the doorways and corners give pretty good cover saves and most of the terrain being up against the wall, so if you were in contact with a wall there was assumed to be enough alcoves, shelves and nooks to hide behind to give a 5+ save or so.

Given the strength of the SMS for this, the XV81 commander should be a strong choice. It's effectively a "better" burst cannon and only costs that of a plasma rifle, meaning the suit load-out will not be that much different in the price of most of our standard load-outs. The commander also has a BS advantage over the broadsides and will cost just about as much.

An XV81 Shas'El is 70 points base, with the requirement that you must take two more hardpoints with it. A broadside is 70 points plus one hardpoint. You get a slightly worse save for a "free" targeting array, relentless, and a huge increase to mobility, and the ability to take additional weapons. Well worth it in my opinion.

Can't have a targeting array though, but if you're relying on marker drones to get the BS up then he'll be in line with his bodyguards anyway. Definitely an interesting choice.

This is irrelevant, even if you rule that support systems aren't allowed on the special commanders (81/84/89) at worst the Shas'el XV81 has the same BS as a broadside with a targeting array, and if you paid the points a Shas'O would have better.

You aren't going to take an XV81 unless you want that SMS anyways, so comparing it to the other sources of SMS is the only legitimate comparison. In other words, saying "a normal commander can take a TA but the XV81 can't" isn't really a valid argument

I still think direct damage from plasma fullsifade is the best way to remove any enemy unit.

If they are termi's you have killed half their squad, if they are gaunts, you still killed half the squad and can probably mop them up with an XV8 assault.

Plasma Rifles kill everything equally. The squad limitations in Zone Mortalis only makes our plasma's that much more utilitarian.

Take two HQ squads of XV89 and you have 2+ saves with TLPR's and you have a lethal interior fighting unit that removes the uncertainty of rending on burst cannons.

It's not like the enemy is liable to be able to avoid rapid fire range either, throw on some gun drones for two rending shots and more wounds and bam.

Alternatively, XV81s with TL Plasma Rifles and a hard-wired multi-tracker bring the same lethality, but also offer a way to whittle away at the enemy units long before the plasma will have line of sight to fire.

Granted, it won't do that much against TEQs (since the rending rule only works on 3+ armor or worse) which I agree will be the most common target, "not much" is still better than "nothing" which is what you'd get fielding any other weapon.

It would partially negate the utility of things like SMS and Biovores (those are the ones that ignore LOS, right?)...

While we're on the subject of ignoring LOS, can you mount Seekers to a Tetra?

Unfortunately no. Neither the updated rules or the Taros Campaign mention anything about equipping Tetras with seeker missiles.

Granted, however I thought the point was the 2+ Armor, if we don't care about that than why not some standard XV8 Shas'El to save points, then throw in some extra Firewarriors for some objective and S5 Rending shots?

Point is, while SMS can whittle away, direct point fire enmasse is still the best method for tau to cause damage. I am just saying those random SMS shots are not likely to make as much difference as a fullsifade of concentrated fire down a corridor. Concentrate fire and remove one unit at a time, that is the Tau method. Bring more guns I say. The moment they kill your XV81 you lose two full weapon systems. Scatter your points out among more guns and they can't reduce your fire power as quickly or effectively.

Basically the added effect of the SMS to the suit sinks too many points into a single model for what it accomplished in my opinion. Especially when it's obvious we are going to be facing tough units, not swarmy ones with the ten man squad limit.

It's a difference in army composition. I brought up the XV81 as an alternative means of bringing SMS to the table without relying on broadsides and it costs just about the same (technically, it's cheaper to field an XV81 than a broadside for BS 4 SMS shots).

I also agree that 2+ saves are going to be vital in the rules set, since the free rending that almost every weapon in the game gets is ignored if you have a 2+ save. However, in terms of raw firepower, the XV81 is certainly one of the most lucrative options. At 105 points, you get the SMS, a twin linked plasma rifle, and the ability to fire both in the same turn. The SMS (as already discussed) lets you shoot at opponents while they are still out of sight, whittling down their numbers before the "final" engagement. I would argue that this amplifies your ability to concentrate fire and remove one unit at a time because by the time the enemy is in range to be shot with your plasma rifle (more accurately, in line of sight) you are now dealing with even smaller sized squads (7 or 8 terminators compared to ten) which potentially frees up extra guns to shoot at the next target after finishing this one off.

I think the tradeoff between no-LOS firepower and the massive boost to durability offered by a 2+ armor save is entirely up to the player crafting the list and that both have their place amongst their respective lists.

I think it's worth emphasising that the "free Rending" rule is fully optional. It's not something that is guaranteed to be in play, so not in itself worth building a strategy around. By all means make the most of it if you and your opponent both wish to play it, though...

Though actually looking at, "Reaction Fire" is optional too. But there doesn't seem to be any mechanism for agreeing which optional rules to use (beyond straightforward agreement)... the first time your Vespid get a 5/6 chance to shoot AP3 guns at the Marines assaulting them might be OK but will you get a chance in second and subsequent games?

"Enemy Unknown" (ie. blips) is also optional. Sadly it doesn't seem super-well thought out... the blip is revealed as soon as it is visible, and the unit it represents is placed in squad coherency, centred on the blip. So... models can (and probably will) simply spring into being right in front of you, just because you now see the blip which is multiple inches behind where the model gets placed? I'm not sure that that works very well.

Personally I would house rule it so each model is a blip, and you move your formation of 'blips' like your unit.

Then, what about SMS? When you fire at a 'blip' does it reveal what they are when the opponent makes the saves?

*shrug* I like the 'blip' rules but like you said it's not totally thought out yet.

IMO for ease of implementations blips should be treated like transport vehicles for units. Deploy/disembark unit within two inches of blip. Unit cannot be targeted while represented-by/onboard blip. Obviously blips can't be destroyed as they are only markers like ammo runts for orks. In the twisting maze of Zone Mortalis when using blips our SMS missile drones will simply get lost and not find the target. Remind me what happens with SMS and night fighting?

Maybe I'm mistaken, but I thought I read somewhere in the rules that indirect fire was not allowed. I'll have to go back and check to see where I saw that. Either way, measuring down the hall and around corners would be an interesting house rule.

I think your thinking of the Barrage Weapon rule under the "Reserve and Deep Striking" section.
I haven't seen anything about other indirect weapon types not being able to fire indirectly.
Every other indirect fire seems to resolve as normal (with blast weapons stopping at the wall).

As part of the blips can't be targetted, I'd also let players have a blip on the board for each unit they have in reserve (which gets removed if the unit then arrives on the board out of LOS, or if the owning players wants to), representing the auspex and scanner ghosts appearing when you're surrounded in these dense conditions - could be a glitch, could be you're tracking the unit in reserve as it makes it's way to the battlefield from another level, above or below you.