The forthcoming greenstuff work will blend the wing points into the pack area some more; as for wing cases, possibly make small flared sections? The large wings having unfurled for full flight.
Casing that is as big as the actual (new) wings would look odd. In a way I think I am influenced by
Genosians more than I initially realised.
Ultimately I'm aiming to differentiate Tau gifted armor portions from the actual xeno itself. On reviewing components and concept art, I'm becoming more convinced the entire torso area including the wing pack are Tau armor components.
If you look at all the joints you see cusped pads with spikes, and a few segmented sections on the shanks. Then most fortuitously, the Vespid has grown complete shoulder armor in perfect arrangement. The segments there, are unlike those about the limbs.

In the original concept art, Cirillo has shoulder armor overtop bulbous shoulder joins. Having chopped into this model, there is an underlying shoulder spot to the upper arms. I think some licence was taken by the sculptor when translating the artwork.
Looking forward to modifying and exaggerating these differences more. As they say a picture is worth a thousand words
- Tael.