I think it would make most sense to collaborate with similar subreddits, which overlap with /r/selfhosted.
/r/selfhosted /r/homeserver /r/homelab /r/datahoarder
These subreddits and more overlap, so to me, it would make sense if these subreddits would come together on the same Lemmy instance, jointly controlled and managed, with each of their own community.
I'm trying to use Mlem iOS app, but it is still in early development...