Keeping with the idea of robotics-relevant answers, another thing to take into consideration for mobile/wheeled robotics (albeit not so much with a wheelchair unless you plan to take it off-roading) is vibration and shock. In reviewing your design, ask yourself: is there anything that's going to come loose? Think connectors that aren't a very snug fit or jumper wires connected to a header pin.
There's been some questions with great answers on Electronics.SE that cover this area at the PCB level:
SMD vs. Through-hole components in high vibration environments
Board Design for High Impact Environments
While this is a pushing outside the scope of the question, be sure to account for disconnect/power loss conditions in software when possible as well. There's not a whole lot you can do on the power side if it's a single-supply system, but if you have multiple subsystems powered off of different supplies, you can monitor supply voltages so that one component can be aware of a failure elsewhere and act appropriately.
If your robot is controlled over a serial interface and the onboard controller can't get some kind of "heartbeat" signal from the host system, it needs to fail gracefully and not go careening down a hallway uncontrolled because the last command it received was "go forward".