Apollo is similar! iirc the only “functional” feature locked beyond a paywall is submitting posts (which you could argue is a pretty big feature to lock away). But I think the majority of users rarely submit posts, and the “pro” tier was just a one-time $5 payment. I found Apollo very intuitive to use and very minimalistic; there was very little fluff to distract from posts and comments.
I think that would be great! I’m sure it’s more difficult than it seems, though, to port over the entire backend to Lemmy, especially with its decentralized nature. Also I’m sure Christian is a bit burnt out after the Reddit fiasco, so I can’t fault him for taking a breather.