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.