As others have pointed out, most hosts will simply de-federate them pretty quickly anyways, and then it will become a useless feature that they turn off.
I suspect it will be one-way anyways, to capitalize on the existing content produced by Mastodon users out there already while they bootstrap. There's no way they'd offer their own content up into the fediverse without the ability to tie it to ads and engagement.
Given the cold reception they've gotten, it will be interesting to see if this feature even makes launch.