Rebuilt the Mastodon backend from scratch and made it able to handle Twitter-scale (500M users, 20M writes/second, unbalanced social graph, etc.). Thus implementation is only 10k lines of code and is also significantly simpler than the existing Mastodon implementation. This clone is running at mastodon.redplanetlabs.com.
Looking at their Github, I mostly see Apache 2.0, which is a bad sign. But this whole thing seems like an advert for their product anyway, so it's likely a nothingburger and won't make a dent in the current Mastodon software's dominance.
Huge questions posed by this development about what the fediverse wants to be and what it can be.
For instance, I've seen some chatter on mastodon about it that are pretty negative, largely because they see the fediverse as a necessarily small place. A counter is that FOSS/non-profit/community run big-tent social media places are actually good and should be taken out of engagement farming big-corps.