Comment by thayne
Exactly. I think the problem wasn't that browsers (specifically Firefox and Safari) were opposed to the idea of html includes in general, but they didn't like the specific proposal, in large part because it still required javascript, and added a lot of complexity for little to no benefit.
I think rejecting that proposal was the right thing to do. What disappoints me is that there hasn't been a more declaritive, simpler proposal that has gotten anywhere.
HTML Imports and HTML includes are two different ideas. HTML Imports was never like what people want from HTML includes.
HTML Imports were shelved because they didn't integrate with the JS module graph. HTML Modules will do that someday.