React will probably just integrate those as they become usable, since React acts as a layer of abstraction between the DOM and your presentation logic.
The only drawback is that it doesn't support custom events out of the box. Instead, you have to manually create event listeners on elements on mount. As far as I can tell, there's no reason why it couldn't in the future though; Web component adoption is so low right now that it just hasn't been something people have complained about.