I think for me the problem with Bookwyrm (and one of the reasons I'm not really looking to move from Storygraph) is that I don't really see services like Goodreads or Storygraph as social networks. I'm more interested in being able to manage lists, recommendations, progress, etc than I am with interacting with users on those platforms. I think they're so specialized, that federating with those types of apps to Lemmy would end up a lot of noise on both that wouldn't really make sense for either.
The only thing I can see making sense for federation for me is maybe being able to follow a reviewer I like via my Mastdon account, so I can keep track of reviews without having to log into the platform.
That's just my thoughts though, but full scale federation vs something more like RSS to me is where the line between social network and app with social features lies for me.