I wish communities could be grouped in some way.

You can do that on kbin now. We just got "Collections" that allow you to gather posts from multiple communities/magazines sort of like a multi-reddit. You can either publicly list them for others to explore or just keep them to yourself if you want. We've also had cross-post grouping for a while which helps reduce the annoyance of "posts four times in a row (or more)" a little bit by collapsing the threads into one block with multiple links and vote counters. It's really useful though if you want to come back to the discussion later and find the other thread(s) -- e.g. check out last week's regular anime discussion threads which got 17 comments on ani.social and 5 comments on lemmy.ml. Jumping back and forth is easy. Hopefully lemmy gets something like that too eventually!