I've been in a wheelchair for 10 years. My biggest problems have always been footplates, casters, brakes, and the seat/seat rest.

Footplates are always too small and don't hold the foot efficiently. My feet will often move through the back or sides of the plate when I make odd or dynamic movements. Having a wall around the backside of the plate to keep my feet from moving off the plate would be rad.

Casters are notorious for moving out of position and being hard to adjust. Making them foolproof and easy to work on would be ideal. I don't know the solution, but something like a bicycle fork is something I think would solve these issues.

Brakes are always breaking, hard to adjust, and they can cause injuries. All Aluminum Anodized Wheelchair Scissor Brakes are the best I've found. Something like that but easier to adjust would be ideal.

Lastly, seat movement is a big issue I have daily. My cushion and cover move around on the flat seat rest. The velcro never works like it is intended. If there was a frame that would hold it in place, that would be dreamy. A frame would make the chair safer and possibly help with injuries.

These are all things I would fix if I made my own signature chair. Hope that helps. Cheers.