This would apply mw.ui buttons styles to most of the essential forms in core. Including edit forms everywhere, history pages, all logs, and (as far as I can tell) anything using HTMLForm. So we'd be applying the new button styles across the board almost universally.
This is riskier and bigger change, but it's what people seemed to want back in the day, when we first started rolling out mw.ui styles in core for login/signup etc. People were extremely mad that we were introducing inconsistent typography and button styles in core. (The typography has since been removed and put in Beta Features.)
The requirement for doing this is that we are much more diligent about doing a design review of every interface this patch touches and looking for major flaws that would impair use. If we're going to move forward with that patch, I want us to not push this out hastily. Let's make a checklist for design review to work through systematically on Beta Labs and also perhaps a separate Labs instance.
This is less risky, but the cost is inconsistency in the UI. I am usually a fan on incremental change, I think Matt has a point here. If we're going to apply to fundamental forms like edit, we should just go ahead and apply the button styles everywhere in core ala patch 52169. The social cost of doing History, Logs, etc. separately is higher than doing it all in one fell swoop.
Matt/Juliusz/anyone: is applying mw.ui to HTMLForm *required* to merge 52169 and apply the buttons to EditPage, History, Logs, etc.? I am thinking maybe it might be good to break the HTMLForm work in to a separate and simultaneous patch, just because the design audit required seems much more varied for HTMLForm than edit, history, logs, revdelete, and so on. Just an idea.