They are already doing it. There are a lot of seemly intentional bugs, I suspect this is a strategy to force users to migrate to the new one. Galleries and some profile features are not supported, and it is (again intentionally) slowed down on mobile.

Reddit jumped the shark already and the current state of affairs is an offense to the memory of Aaron Swartz. Problem is that a new mass migration (as happened in the Digg→Reddit move) is way more difficult due to the inertia and amount of content available. I just hope that, when it finally happens, it would be to a distributed or federated system -- Lemmy.ml seems to be the most promising for now.

Their CSS is completely broken and nearly unusable on mobile.

They're clearly "improving" it.

Not to justify how completely terrible it is, but you can click the accept once and never see it again.

Also teddit.net, which I find even faster and lightweight without JS.

On desktop, yes. On Mobile, the normal reddit is ridiculously obnoxious unless you tick "desktop site".

It's absurdly laborious to have to click "Continue this thread" on any subthread with more than a couple levels of replies, which takes you to a completely new page. A genuinely awful experience compared to the old site, and for what?