Instance blocks have been available on several other projects for at least a few years now; we just have never used them because as a filtering technology it is irreparably flawed. You need go no further than hubzilla to find out how badly it is flawed. There your identity is nomadic and is not tied to any particular site.

Incidentally, several projects implemented site blocks in response to an influx of the free web by Islamic State a few years ago and started sharing videos of people getting their heads chopped off. But IS members didn't setup their own sites where a site block might have had marginal effect. They just signed up at popular instances where site blocks would never work.