Other 'obvious' design improvements that seem to be missing:
* Wheel-assist - an electric motor pushes along with you to stop you getting tired arms, but still give you the feeling of direct control you don't get with a typical joystick controlled electric. Little 100 watt brushless motors with controllers are only $3 now, and that would be plenty of assistance for going up ramps.
* Auto brakes - a sensor brakes the wheels whenever a hand isn't touching the rim of the wheel - and that can be a software only feature enabled by the above assistance motor...
Etc... It seems wheelchairs are crazy expensive yet don't have most of the features an undergrad student would build as a 'for fun' project.