No big deal on splitting the community in half? Matt will not go and you will have half the people supporting him, half forking the project. Actually less than half on each side, when you count in the people that will completely leave the ecosystem...
Sure he controls a scary amount of the ecosystem NOW, but we've seen big vendors express interest in hosting repositories, and major plugin vendors move quickly to secure their distribution and update models.
My tiny agency has already mitigated many risks and shifted our support towards developers who see a future PostMatt™
We'll be fine because WordPress belongs to us, not Matt.
Sure, WP isn't going away overnight. But it's dead in the water at this point. Literally like a dead whale, still going to support an ecosystem for some period of time. Though, it's peak is behind us and the unwinding was accelerated immeasurably.
They aren't acquiring new customers faster than they are losing existing customers. Squarespace and similar products are to eating it's proverbial lunch among a large portion of their audience (small to medium businesses who just want a website that is easy to update).
If some of the biggest hosters forked wordpress and started adding features that their customers are asking for, that wordpress the organization were ignoring or slow to produce, I think it would be a good thing. Providing wordpress the org with some motivation to compete.