API proposed by Chrome: Declarative partial updates

Very odd proposal. The new element syntax is perhaps the boldest choice. I wonder why they thought that was necessary. The idea of using this to defer rendering elements is also odd. So this would use a http long polling style? It really goes against several decades of progress in the web platform, where by now it's long established that you do this sort of thing with xhr. I'm amazed that they even put this in chrome, let along are saying things like "let sites use this new functionality right away even before this lands in other browsers" as if it's a sure thing.

Is this a Google-only proposal? Has Mozilla provided their thoughts on the matter?

So htmx?