Personally I'd be interested to see what would happen if Sony/MS did what they could to make keyboard/mouse experience as good as possible on their consoles (I'm writing from a position of ignorance on the state of mouse/keys with current consoles) and encouraged developers to offer a choice in inputs, so that the locked-down machines can become the place for highest confidence in no/low cheaters. If other people want to pay through the nose to go beyond what consoles offer on the detail/resolution/framerate trifecta then I'm sure they could do so, but I really don't see how you lock down an open platform. That challenge has been going for decades.
Well, Nintendo's latest console comes with two mice that you can both use at the same time even.
> I'm writing from a position of ignorance on the state of mouse/keys with current consoles
I'm far from an authority on this topic but from my understanding both Sony/MS have introduced mkb support, but so far it looks to be an opt-in kind of thing and it's still relatively new.