It would be interesting to see #WordPress fork hard in response to Automattic's clear desire to have their open source cake & copyright-restrict it, too.
I'd find it fascinating if someone did a database-compatible fork with a wholly new front end. That basically happened w/*Nuke in the early aughts. (Hell, when I first looked at the WP database schema I was like 'holy crap this is PostNuke!' I still think they basically took a *Nuke schema as a starting point & wrote a new front end.)