JSX was such a breath of fresh air after having written and maintained apps which used both of these formats for years (and also having written a library which supported both of them for reusing the same templates on the server and in the browser) - it's the commas! I'm glad it's everywhere now.
But that was also back in the days when trailing commas at the end could break things, JavaScript editor support was relatively poor, and tooling wasn't where it is now (knowing your code is once again valid because the autoformatter just kicked in).
Mastro looks like what I do for my offline-first, rendered from Service Workers. I just compose html template string literals and stream them back to the front end. The lib I use for HTML is a bit more powerful though. It is a very elegant way to program.
Speaking of writing JS instead of JSX or your example, I like the vanjs.org approach: