You're describing E4X. E4X and JSX are both XML-inspired syntaxes, but beyond that have relatively little in common in how they function.
E4X was supported by Firefox for a while, but I think support was removed.
The way I see it, syntax sugar can be part of the language proper.
For instance classes in JS are sugar syntax to define a function that defines fields in this and prototype members of this function.
Arrow functions are sugar syntax to define functions bound to a specific this.
async / await is sugar syntax for promises.
for..of is sugar syntax for iterating over an iterable.
Think it may have being easier if JSX is just included in ES as a standard. So yes and no, JSX introduced by FB via react is a just a syntax sugar, however the original JSX is a meant to be a ES standard, with each node as a tree structure.
https://www.ecma-international.org/publications-and-standard...