Also be careful not to point out that "keyboard noise" is the crux of the issue, since then you'll end up with those employees being told they can't use their nice keyboards that they probably paid a lot for just to use at work, which will result in said employees really, really not liking you if they find out it was you that complained.

Exactly. That's a great way to poison a relationship with a coworker.

Any source for the statement on RSI? I googled but just found anecdotes.

Anecdotes are the best you're going to get on that. Who's going to fund a serious scientific study on the effects of mechanical keyboards on RSI? The mechanical keyboard makers comprise a very small, niche industry these days.

The anecdotes are correct: with a proper mechanical keyboard, you don't have to bottom out on the keys, and only have to press enough to make them click. Once you retrain yourself to do that, then you're putting a lot less stress on your fingers, compared to rubber-dome keyboards where you're forced to mash the keys down until they bottom out.