...and face a fully justified user/dev revolt that makes Mozilla's worst day look like a single angry tweet. Remember that there's a massive paid ecosystem around WP plugins & themes, not to mention the stuff Automattic sells (hosting, their own plugins, etc.)

They can't afford it, and most people don't want it. I think history shows that taking flexibility away from something popular because of its flexibility is not good business. At least you can install a plugin now and completely sidestep this awful 'site builder'. If that goes away, hoo boy.