I haven't used Vue (and definitely not TS with Vue), but considering how easy it is to create type definitions for libraries written in ES6, if using Vue + TS is awkward (assuming its not because no one wrote a type definition for it), the only way it could make things better for TS users is with some refactorings to make sure types "follow along", and that totally would affect ES6 users. Anything that does not affect ES6 users would not affect TS users either.

An example of this is how in Redux, anything that uses the state in TS needs to add an annotation to type the store, because its completely decoupled (and thus theres no way for the state type to "follow"). Any way to make it follow requires some API changes (eg: creating mapStateToProp functions by calling a method on the store)

He's possibly meaning that if you completely rewrite framework it would lead to something like what happened to Angular when it was rewritten and promptly lost huge number of followers/users?