I would imagine that for people that actually care (whose threat model involves governments targeting them specifically), then they're aware of all the tradeoffs involved and can make informed decisions (and know how to use more secure, harder to use platforms). For everyone else, I think "e2e encrypted by maybe twitter is lying to you" is no worse than the current state of play.

We do, but that would require the company to lie about what they are doing with the app. At Twitter's scale it's very possible that someone would notice and leak that.

The goal as I imagine it is to go from "Hundreds of Twitter employees can definitely access my messages today and anything I've sent and received up until now" to "Twitter will likely need to perform a MITM attack to read my messages starting from the moment when the attack was performed. Maybe they have a secret backdoor, but it's probably too valuable to use on my cat photos".