I might be totally and completely wrong, but changing everything does not help anyone except scratch the itch of the framework's designers. I'm pretty sure this is all with the best intentions, but this would be a disaster similar to how Angular suddenly changed everything . Not against change, but the API is fine. Just iterate and evolve it. disclaimer: Big fan of Vue, early user and conference attender..
For me, working in a large project with TypeScript vs one in vanilla JavaScript makes all the difference in terms of how maintainable it is. The number and the nature of the tests I need to write for such project changes, the IDE tooling available makes development much more pleasant, and I generally feel like it is harder to write code that is buggy, because a large amount of potential errors are avoided through use of the type system.
Whether or not they've made the right decision with this split is a different question that I can't answer.