At Develop last month I got talking to the guys on the stand for the SpecialEffect loan library project 2011-2013. @SpecialEffect is a charity which aim to make all games accessible to everyone. The library aspect is to provide specialist controllers, emrging technology solution and software patches for young people with vary degrees of accessibility issues with games in particular.

SpecialEffect Loan Library Project from William Donegan on Vimeo.

The charity points out that many games can be too quick or difficult to play for many young people with disabilities. They aim to either provide new interfaces or changes to the games, or actually tell people which games already are playable with suitable settings for specific needs of a specific audience.
If you think about it this can be as easy as providing subtitling on dialogue to hearing impaired, or enough changes in speed and skill level to allow the game to still be enjoyable and a challenge.
On the stand there where examples of console games adjusted to take single oversize reactive button input, or shoot em ups that had context sensitive directions. It was very inspiring and thought provoking.
We have often talked about the affordances virtual worlds give us, a digital environment, haptic feedback etc all providing ways that anyone could interact. The reality though is that accessibility is not a focus of mainstream gaming, but Specialeffect are pushing the right direction.
There is also a games database called gamebase that indicates what features existing games already support to help people understand what can be done with them.
It is well worth checking out, and considering.