All of those examples are significantly better than the proposed mockup, the huge issue I have with that mockup is that it tries to be both “buttons” and “radio boxes”, pleasing both ends up pleasing neither.
Take a look at Twitter as well
Personally I am fine with a “modernized” list of radio boxes or check boxes. I am against an un-themed form, I think it would look horrible.
I am also totally for changing the markup to use a FORM with INPUTs as opposed to the UL / LI scheme we are using now. It seems much more correct.
I get the complaint here just very much dislike the UX of the proposed changes in the OP.
I think the Twitter styling is fine, modern and definitely something I think we could emulate.