Gameplay is something we haven't figured out for non-handicapped players. My gf was complaining about a game, all movement is controlled by using the mouse. Move it forward to walk, move sideways to turn, restore to where it was to stop turning.
If you're disabled and would rather use keyboards, it's not an option in this game. If you're not disabled, it's still not an option.
Ensuring all controls are programmable would go a long way to helping everyone, not just the disabled (or just my gf, which would improve my standard of living).
Early in the process, someone decides the game should be controlled this way, and it affects a lot of other decisions. You can't make a WII game that suddenly requires a keyboard to solve a puzzle, or switch weapons fast enough to defeat a boss, so the gameplay sits on those decisions.
Is it possible to lock onto a target and walk around? Or do you omit locking and strafe instead, making the user strafe and rotate simultaneously to avoid being hit while remaining on target? Are the fire and strafe/lock buttons ones you can hold at the same time (preferably different hands) or do you have to hold both the triangle and x buttons while pushing L2? These things need to be abstracted away so anyone can play any game with any input device. A NES controller with USB hack on the end, or mind reading, or voice, or keyboard, or mouse plus anything else, should be equally possible. Not equally successful as I've pointed out, but possible.
If one particular board or puzzle requires certain faculties, that should be clearly labeled (parkinson's might cause problems playing because the aiming system sucks, blindness might leave out details because it's supposed to be a surprise reveal but we didn't include subtitles because no one's talking).