Have you considered a feature like “sibling community”?
What I mean is, for example, car community on server 1 marks itself as a sibling community to a car community on server 2. Similarly server 2 marks itself as a sibling community to server 1, ie it is two-way.
When communities have been linked bi-directionally, any post and comment are shared between the two sibling communities.
This would allow bigger communities to form out of smaller communities, thereby preventing discussions from being fragmented and showing the true size of Lemmy, across servers.
Especially given that Meta needs federation to comply with the Digital Markets Act.