I’m not sure its in the works, but it needs to be very well thought through prior to implementation.
Like, what makes sense to me would be a way to ‘sub-federate’ two or more RSS feeds into one. IE, if lemmy.ml and lemmy.world are federated, lemmy.world has the option to ‘sub-federate’ c/memes from .ml with c/memes from .world, or at least the moderators would have that option. You may only want there to be a 1:1 with sub-federation (IE, you don’t want many .world /c’s subfederated with one .ml /c or you would get a (possibly extreme) duplication of content. But this could be option and up the the lemmy instance to decide how to configure.
Regardless, the ‘wideness’ of the way the network is set up with many nodes and relatively few edges is the primary issue. It can’t be resolved with just ‘more engagement’. Reddit doesn’t suffer from this issue as much because there its only one order of dilution (one reddit, many subreddits). Lemmy suffers more because there are two orders of dilution (many lemmy, many sublemmys). Its also important to note here that Reddit did not have subreddits to begin with. They came later, which helped them build the critical mass to overcome the diffusion problem.