I don't think it matters if some platforms fall out of use and others rise to prominence. It could change several times in the coming years, but we already support almost every major platform, so we've got it covered really.
The web has legendary backwards compatibility for widely-deployed features - you can still correctly view the original Space Jam website from 1996! That's a website over 20 years old. Newer features tend to chop and change more, but mainly as the spec is refined to make sure it's robust for the future, and we update regularly to keep up anyway.
I recently saw a benchmark where the C2 engine in Chrome outperformed a competitor's native engine on desktop Windows, and approximately equalled another which compiled to C++. This pretty much confirms to me that the performance argument for native, or this idea that "HTML5 is slow", is totally dead now. Having a native engine does not guarantee good performance, and modern JavaScript JITs are incredibly potent. For years I've already noticed that almost every performance complaint comes down to hardware limitations (e.g. GPU fillrate), and people simply knee-jerk blame HTML5 without understanding what the real problem is. So as far as I'm concerned, we're there: HTML5 has native-grade performance now. There's nothing significant to gain by a native port.