What would be great would be having some serial port commands to handle USB and bluetooth. Then it'd be reasonably easy to implement support for say head-trackers and other various gear. A GUI designer would also be nice - though that is more of an external tool. Better support for video would also be handy. Not just playback, but also using a phone or tablets cameras to record and even do simple edits, like trimming the fat at the start and end.
Can't think of anything else right now. We just got UTF8 encoding at long last (yay!) and True-Type Fonts (yay! though there have been reports of some issues with these, so I am using bitmap fonts for the time-being). So all in all things are shaping up nicely.
As for AppGameKit and speed. Well, AppGameKit follows more or less the Java-the-Mess way of doing things. The runtime (binary) is actually a Virtual Machine that sits between your compiled bytecode and the hardware, why we got such great cross-platform abilities with AGK. However, unlike Java the Terrible, the AppGameKit VM is pretty lightweight and optimized to move graphics around (using the OpenGL 3D library).
So in terms of raw speed, AppGameKit sits somewhere between languages that compile down to a native binary (like C++) and interpreted languages (like Python). Exactly where on that scale I do not know. It'd be interesting to do some benchmarks. Like say find the first 1000 prime numbers in C, C++, Go, Java, AppGameKit, Javascript and Python. Incidentally, I think that'd be more or less the order the results would come to.