Mouse affordances don't usually ruin it for keyboard preferrers. Keyboard shortcuts and control are often an afterthought or downright written off because "they can just click" but thats down to laziness or lack of care than some hard and fast rule. However, a keyboard affordance is usually invisible, and a mouse affordance isn't, so they can very happily co-exist without affecting one another. For instance, the Alt modifiers in menus in classic Windows, those have almost no effect at all on anyones ability to click the menu item with a mouse.

Touch affordances and UI does have to be visible, and there is only one screen. So the touch affordances and mouse affordances are mutually exclusive: targets get larger, padding expands, UI gets dumbed down, etc etc.

I can't think of cases where mouse affordances necessarily, intrinsically make things worse for keyboard users.

Of course, there's the extremely common case of keyboard support being half-assed or missing from GUI apps. But that's not mouse affordances making things worse, that's developers just not having the time or inclination to have great keyboard support.

Whereas, touch affordances seem like they'll be a lot more disruptive.

Just look at Windows 8?