We pretty much had this when the first reliable Mastodon<->Bluesky bridge came online. The Fediverse side protested and made the entire system opt-in, making it practically unusable because people that don't have a favourite Linux distro don't know what a fedi is and why they should bridge to it.
When this goes live, I expect people to treat it the same as every other sizeable social media joining the Fediverse, with outrange and block lists.
To prevent annoying trolls from digging through my post history, mostly. I've seen people do this on Lemmy, one person even had a stalker that would go server to server to reply angrily to their posts because he felt "wronged" somehow. Plus, nobody is reading this stuff after a month anyway, the only readership of old comments is AI scrapers trying to steal my words for their algorithm.
Of course, deleting stuff on Lemmy doesn't mean actually deleting anything. You can trivially ignore deletion requests as a server and some seem to keep old copies of deleted content.
There's no automated way to do it with Lemmy so I've written my own automation tool that occasionally runs.
We pretty much had this when the first reliable Mastodon<->Bluesky bridge came online. The Fediverse side protested and made the entire system opt-in, making it practically unusable because people that don't have a favourite Linux distro don't know what a fedi is and why they should bridge to it.
When this goes live, I expect people to treat it the same as every other sizeable social media joining the Fediverse, with outrange and block lists.