I do not object to "federation" of #Mastodon to other social platforms, so long as the connections are TWO-WAY and aren't just (in theory or practice) mainly a mechanism to firehose posts from giant platforms without giving replies from Mastodon equal footing with native replies on those platforms.
This must also include the ability for users on those other platforms to subscribe/follow users on Mastodon (and for Mastodon users to follow users on those platforms), and provide equivalent mechanisms for abuse control including blocking, etc.
Otherwise, it's a trap.