Buff shadows, I think it's a great trouble for a PC or great console not it's too much problem, but for a "simple" device like a mobile it's a very hardest task... depend the kind of shadows too... (for this I think it's better paint over the surface a simple black Sprite).
Another good thing will be 3D physics... I know you made a port of Bullets (I try too, but my C++ skills not are enough), this will be awesoming... well your port works, but not for mobile devices

I read sometime ago an idea to make a Shop, really I think this not it's a great trouble, here we are some people we know do 3D, the problem it's how many users buy chepest models... in fact Shiva 3D open a self market for this...
If it's possible to put a maketplace here can be interesting, not only for us.. because how you can sell the model in .DAE .FBX or another formats, perhaps people from another sites come to here to buy... or not.