I'd be worried about misuse. I can already see developers wrapping every element with HeroElement because they think or were told it would "speed things up". But of course if everything is a hero, nothing is a hero.
It sounds like the idea here is mostly for things like "hero slideshows" at the top of the page, some sort of way for speeding up the performance of sites that utilize that pattern because those can get heavy. First I'd examine what patterns are available today to not run into such a optimization bottleneck in the first place (lazy loading).
I feel like a lot of emphasis is put into rendering "above the fold" content, but there is no fold in web design. If your websites supports the URL hash to deep link half way down pages, which it should, then a user might not land at the top of the page at all. So I would be considered with an element that is off canvas being "sped up" because that means the things I'm actually viewing are slowed down.