all new posts and comments inside that community will be mirrored to your instance

And that’s my biggest issue w/ Lemmy. It seems to scale okay, provided you have enough users to make all that traffic worthwhile. However, I’m unlikely to actually self-host since I really don’t want a copy of literally everything I sub to. Ideally, I could host my own authentication server and only the communities I host (which would probably be 0), and I’d just fetch whatever I needed from wherever it’s hosted.