Templates/hierarchies improvements; Bug fixes.
I think there much more core and useful features that can be worked on (render masks, for example)
This engine is obviously not meant for 3D and wont have sufficient set of futures for that. Its cool to have some basic features, but that's it. And it would be sad if instead of improving main 2D part already small team of devs would spend more time on 3D (and it will definitely take tons, TONS of time to have even some basic 3D features other engines have)