Xbox have implemented a text to speech API for game developers. As of now, game developers can choose to add text to speech to in-game menus and elements.
It doesn't work automatically, but it is fairly straightforward.. send a piece of text out to the API and the Xbox will read it out according to the player's narrator preferences. Unless the developer wants to choose a specific voice to fit with their game, in which case it uses that.
So if you know of any games that are mostly accessible but crying out for some voiced menus, now is a good time to ask the developers. Xbox will work with them to make it happen.
If you know a developer who is interested and wants to speak to Xbox just let me know via [email protected] or @ianhamilton_ on twitter, I can introduce them to the right people.