I won’t speak to the technical merits of MCP but I will say this: it doesn’t matter for many use cases, in particular consumer tech.

The entire digital consumer economy is built around ownership of the screen real estate, due to a simple reason: ads. Whoever owns the sidebar sets the rules, period. Web2.0 was all about APIs (usually Rest/json) and in hindsight we see a clear distinction on where they’re used: in commercial B2B apps. Conversely, big B2C players shut down the little open they had - Facebook, Gmail removed their XMPP support, and these days Twitter etc even gatekeep content when you’re not signed in or using the app, and aggressively fortify against even basic scraping. When you’re using other clients, you are bypassing their sidebar, meaning their opportunity to deliver ads.

So no, your iOS apps and Twitter are not gonna ”open up” their APIs in any way, not through Rest and not through MCP, simply because it goes directly against their incentives. The exceptions are (1) temporary to ride a hype train, and (2) services you pay money for (but even that is wishful and hypothetical).