Humane Tech Now, if other standards are chosen, there's nothing stopping people adding support for these standards to their projects. IIRC Friendica for example does both ActivityPub and whatever Diaspora uses.

The "corporate fedi"... Well, the most important part, decoupling the data from the presentation/UX, would still happen. Gmail is the dominant email provider, yet I can still self-host my email server and interoperate with gmail, and I can use gmail with a third-party mail client of my choice (which I do — haven't seen the web UI in ages). This ability of the users to use their service in a way *they* want would seriously undermine their existing business model already.

The current business model for Facebook et al consists of tightly controlling the presentation of the data they have so as to:
1. Manipulate users into spending much more time on their properties than necessary — "engagement". Algorithmic feeds, forced recommendations EVERYWHERE, meaningless notifications like "tell your friends what you're doing, post a Facebook update" (I'm not making this up — I have literally received this back when I had the app installed), purposely convoluted UIs (they had a feed redesign project long ago, scrapped it because the new design was so convenient that users clicked less, and spent less time on Facebook).
2. Ads. Inescapable, creepily targeted ads everywhere.

If they're forced as little as to open up their API and allow people make third-party clients, they've already lost and will need to seriously rethink their business model. That's because third-party clients take away this control over presentation — first thing such a client would do is filter ads, recommendations, and other content unwanted by its users. Federation is simply a further extension of this where you don't even need a Facebook account to interact with Facebook users. That would just hasten its demise. Which is long overdue anyway.