It's good when someone advocates for what they believe to be progress on the web platform, but it's not necessarily clear that this would be progress. And that line in particularly is amusing because we absolutely don't know what good syntax for templating looks like — that's why there's so many different options.
JSX is certainly the most popular because it's used in the most popular framework, but it has some very clear weaknesses. In particular, it has very clear semantics for a React-like, VDOM-based framework, but those semantics do not work as well for other kinds of framework.
For example, you mention control flow via ternaries/`.map`. This works great in React, where the entire template will be reevaluated every time any input changes. However, frameworks like SolidJS or Vue in Vapor mode work very differently, and typically evaluate JSX only once at component mount (or at least, as seldom as possible). To support these, these frameworks need to use either special components like `For`/`Show`, or directives like `v-if`.
There's also the issue of how to evaluate JSX. In theory, JSX is flexible, in that `` can be converted to any call of the form `h(Cpt, {prop: expr})`. Again, that's not true for SolidJS or Vapor mode Vue — in both of these frameworks, `expr` cannot be eagerly evaluated, so the traditional transforms just don't work. Both of these frameworks therefore have to include their own custom plugins for handling JSX correctly.
The author's suggestion to also use signals as a state mechanism suggests they're imagining something more along the lines of SolidJS. That's an odd choice (it's my personal go-to framework, but it's also very niche), but it also implies, as discussed, that JSX-in-the-browser wouldn't behave like JSX-in-React. From experience, that will cause problems! I've worked with React developers before who've really struggled to use SolidJS because of precisely this issue.