I think the idea of that is reasonable. If I used XSLT on my tiny, low-traffic blog, I think it's reasonable for browser devs to tell me to update my code. Even if 100 people like me said the same thing, that's still a vanishingly small portion of the web, a rounding error, protesting it.
I'd expect the protests to be disproportionate in number and loudness because the billion webmasters who couldn't care less aren't weighing in on it.
Now, I'm not saying this with a strong opinion on this specific proposal. It doesn't affect me either way. It's more about the general principle that a loud number of small webmasters opposing the move doesn't mean it's not a good idea. Like, people loudly argued about removing <marquee> back in the day, but that happened to be a great idea.