Well, from my own point of view, I really don't care what forum software is used here - though to be fair about it I am aware that I do not post as often as many users. I'm interested in Discourse, partly because I like to see someone take a different take on things, and partly because I have been considering implementing it myself.
Speaking as a developer though, can we all (TDWTF & Discourse) just cut the abuse / sniping. It serves no-one's interest, and it's not professional.
The final decision is down to Alex - it's not a democracy. I think Alex has to carefully consider that he risks alienating and losing SOME users, and that some of those users likely contribute a higher proportion of the content than might be expected, but that's his bag. It's his site.
Personally, I don't plan on rage quitting based on which forum we use.