Mastodon should just implement the quoted toot feature and forget about it. Obviously it’s useful given how much it’s used on Twitter.
This should answer your questions.
"[...] ActivityPub-based federation was removed and will be replaced with our own protocol that scales and is more secure."
"Federation is the last thing that will be built into Social. Gabbers, in very large numbers, simply didn't use Federation (or care about it at all). [...]"
Bitcoin Maston Instance