Even if starting out doing http connections one to one like vote rows are replicated today. This would at least cut down the PostgreSQL storage of non-local instance votes in favor of having just one single row per comment and post (which is already existing overhead, even for non-local post and comment).
The home instance of a community (which owns the post, which owns the comment) is the only place to have the full history of activity given how Lemmy 0.18.2 has no backfill procedure for activities before first instance subscriber to a community.