Number of (active) Lemmy users seems to stabilize and I think this is a great thing. Indeed we got a lot of users when reddit shutdown its API (I was among them despite being a long time oss user), many have left, but the community seems now to stabilize to ~ ½ of the big grow in june '23. I think this is very nice for lemmy, we can be proud of this project.
The stats come from: https://fedidb.org/software/lemmy
Im not sure how up to date that roadmap is, but the pull request for group support in Mastodon has been open for 1.5 years now. And for reasons I dont understand it was made intentionally incompatible with Lemmy. So dont get your hopes up.
Roadmap is updated recently. They did a poll to establish priorities given the recent surge in users sometime around November.
Coming back to this topic after some time. What do you think about the private group criticism of FEP-1b12? Is this resolvable without leaving the standard set by FEP-1b12? My first instinct is yes, but I imagine you've given this a lot more thought than I have.
Private groups are definitely possible, in fact we are planning to implement them in Lemmy soon. I already made a pull request for local only communities which is a first step in this direction.