Reddit had something similar with ‘multireddits’. It was basically just a way to group multiple subreddits together. You could either create a multireddit for your own use or you could share it for others to use also.

For posting you would still have to post to a particular subreddit. But for reading you could easily view all the posts for the group.

Right now, you can only view Lemmy as ‘Local’, "All’ or "Subscribed’. It would be nice if I could have more control over that, and view for example ‘all the movies and tv communities’.

I think this is especially true since right now it tends to be the case that the high traffic communities tend to drown out the smaller once. If I look at my Subscribed feed, it is dominated by a handful of communities (News, WorldNews, etc.) since they are getting the most posts and comments.

For example, one can imagine a mathematics & physics oriented instance where LaTeX is available, or a chess-only instance where you’d have things like chessboard.js to allow members to post chess diagrams etc…

An interesting idea. But the problem with that is that the custom rendered content would not federate properly, so such communities would only really be usable to those on that instance, which destroys the whole point of being federated in the first place. Unless they were able to implement some sort of ‘graceful degradation’ so the content was enhanced on the main instance, but still serviceable on other instances.