@julian I think the best way is to subscribe to the the mailing list and reply to state your interest to participate and in what way.
I am not sure about how-to-subscribe for this particular list, and I'm not subscribed myself. I created the socialhub topic to draw attention to fedi dev community there.
See that there's a 'reply' icon on the thread, which pops up an email form. Dunno if that works. #IETF Search finds zilch searching for #WebFinger weirdly enough.