hyperscript is about as close to a middle ground as we can get. It's compatible with JSX for the folks that really really want to see angled brackets, while still being uniform javascript like other API variations (div(), html`<div></div>`, etc). The lit-html syntax is not bad either, but template strings did not have as widespread support back when mithril originally came out.
Since the framework isn't interested in chasing trends and since it provides extension points via lifecycle methods, there's really nothing novel that needs to come from the framework itself.
I know some of the more popular frameworks make it seem that webdev is constantly in churn/evolving, but if you look at React for example, other than the hooks paradigm shift etc, it hasn't really changed all that much in scope over the years either (the same can be said about other libraries as well).
For example, Mithril could easily be used w/ coffeescript when that was still a thing, and people use it with typescript these days too without much fuss since TS is also a project that decouples well. And this is with zero changes to the framework. You can integrate dragula or plupload or google maps or whatever via lifecycle methods as you always could too.
So, TL;DR: I think the focus still remains on making it as stable and robust as possible
https://github.com/DefinitelyTyped/DefinitelyTyped/blob/87f2...
It's probably because I've been reading and writing HTML for +20 years though.