You can be fairly certain GWX 3.0 will build upon the already great features in its predecessors. Fixing known bugs and other mistakes is a given.
As for new features?
My money is on a much improved version of the LifeBoats mod (with Rowers included), Tomi's fantastically crafted VIIC, and a playable Type XXIII.
The rest is also a matter of much speculation ever since news of the impending release of GWX 3.0 was made public.
The one certain fact you can count on is GWX 3.0 will be another amazing work from The Grey Wolves!