I believe that Tor Project ought to encourage bulk data transfer through and among onion services. That would add chaff to protect other users. There's resistance because it would increase network load. However, there's considerable excess capacity for middle relays, because they attract so little attention. There's even excess capacity for entry guards, and policy could be changed to increase that. It's exit relays that are rate-limiting, and onion sites don't use them.
Using multiple Tor instances with MPTCP, I've managed 50 Mbps between onion sites with gigabit uplinks.
Using multiple Tor instances with MPTCP, I've managed 50 Mbps between onion sites with gigabit uplinks.