Its a difficult balance to strike. While accesiblity is a good thing by itself if it castrates the play mechanics it can make the game less fun.
I look at it like a piano. Most certainly you can play one handed, in fact any simple melody can be done with one hand. But that's simply not as enjoyable as playing with two hands.
Now say you want one handed (we'll say right hand) people to be able to play a two hand piece. You've got a few options:
1) Give them the option to "build" left hand macros and add in a few extra functions to fully flesh it out and fit different parts of the song thus never playing it perfectly but usually good enough to be functional. They can't have AI built into it but can still get relatively complex. This still will tend to favor a two handed person but doesn't bar a one hander from playing.
2) Have left hand functions taken care of automatically with minimal user intervention. Works but kills some options for customization and uniqueness, makes it considerably less enjoyable for someone who wants to play with their left hand.
3) Dumb down the songs so one hand can play the whole peice with a little difficulty and two hands make it increadibly easy. Can make it frustrating for one handed people and boring for two handed people.
At the end of the day the two handed person just wants to play the damn song on a piano as it is. So the question is, how far do you take making the piano accessable at the expense of diminishing the experience of the two handed person?
For me, trying to fleshout making buttons and complex macros in as user friendly ways as possible and having open swaping of hot keys for practically every type of movement and interaction with some extra tageting/camera functions built in is about as far as you can go before you start penalizing the experience for non-disabled. After VG has a lot of its more major bugs fixed I would hope that they implement these but with their limited resources I'm not about to hold my breath either. The macro creation as it currently stants is OK but simply not good enough and there isn't things like binding camera to target (which was already mentioned) etc. How hard is it to fully flesh things out so a disabled person can play enjoyably? No clue.
Dumbing down the game or stripping away options that may be too difficult to use is not a good solution. But I think most of us could agree on that anyway.
That said, a one handed person can still try to play the piano, but they would possibly get much more out of playing a trumpet.
Its a sensetive issue for a lot of people to be sure, but there are good and bad ways to go about it and it has to start with the realization that no matter how smart and capable you are if you are unable to transmit those thoughts into functional actions you will be limited in some way shape size or form compared to someone who can.
I don't play FPSes online, I have a head for strategy, not insane reflexes like some of the people I've run across that ritualistically turn me into to cannon fodder, I'm not terrible but I simply am not on par with them. I realize this, I don't get mad at the game for catering to people with better reaction time than myself, I play something else.
Always good to take a few steps back and look at a situation for what it is. And increasing awareness of disabled people is never a bad thing.