For now I subscribe to multiple communities, but I really hope the Lemmy devs figure out a way to let each user create a community group.

The way I envision it is that you can create a group where you can combine communities on your end, and you can then cross-post to these communities when you post to that community group.

On the other hand, there would need to be a way to ensure that cross-posts aren't generating a ton of duplicates to those subscribed to multiple communities, and I'm not sure how the comments on these cross-posts should be dealt with. Maybe the comments should be kept separate per cross-post, or maybe if you have these communities in a group there could be a way to display the comments from there multiple posts together, to ensure all those crossposts have a change to get some interaction on other instances?

Then there's also the possibility of spammers abusing the system.

There is still place for improvement.