Of all the nerdy things I'm excited about, the prospekt of making bug reports to FOSS git projects through my Mbin or Mastodon accounts is certainly on the list. I have so many accounts I made just for a single bug report. This will be great if/when it takes off.
I'm personally really excited about being able to effectively move control away from central hubs such as GitHub ensure a different model of governance.
GitHub is currently okay, it's a bit slow, the UI ain't that great but it works. However, it is a prime target for enshittification. It's a large platform (and besides that also owned by a large public company) with an extremely large userbase, with a non-trivial cost to leave. People are simply much more likely to contribute to a project if they 1. can easily find it 2. can access it without having to create an additional account 3. have a functional, familiar user interface. Federation solves 2 of those issues and perhaps also point 3 since Forgejo is afaik still one of the only ones to support it.