+1, a multireddit workalike would be really handy for managing similar communities that are hosted in different places. There are already a bunch of communities that duplicate the same effort that aren't federated with each other.
Further, it would be even more helpful if Boost let me backup all of my community subs and multicommunities somewhere like Google drive so I could restore my personal feed if I were forced to move to a new server at some point. I'm pretty sure there's going to be some lemmy host attrition over the next few years, we probably won't lose .world or .ml but I can already see this being a big problem for active users who happened to sign up on a smaller instance that eventually shuts down.