Comparatively, the multi-communities idea, I’d guess, is a much more natural extension as it’s really just allowing a user to have multiple sets of subscriptions, which is an already established process/feature.
I guess that’s where I see the issue and maybe were talking past each other a bit. I think if its community moderators that ‘subscribe’ their sublemmys to multi-communities, that could work. But if its on individual users, its not going to solve the fundamental underlying issue of discovery.