Second, "GPU-enabled JavaScript" has already taken off. Ever used Google Maps or Google Earth - both use WebGL heavily? Or maybe you read the NYTimes who occasionally produce pages with a heavy WebGL focus[1].
[1] https://www.nytimes.com/interactive/2015/01/09/sports/the-da...
The biggest problem with the WebGL compatibility issue is that it is unpredictable. We don't know which devices work until we open the page. Maybe I am expecting too much, but this degree of inconsistency shouldn't happen to hobby projects neither.
Are you claiming that there's less effort in coding up a native graphics program that works across all platforms?
Certainly native has the edge on performance (WebGPU will shorten the gap a bit), but on ease of multi-device compatability? I could be convinced, but it seems hard to believe. The whole idea of the browser (these days) is to make cross-platform stuff easier to develop.
If you restrict yourself to the basic parts of WebGL 1 your app will work almost everywhere, as compatibility is excellent on all recent phones and OSes.
There’s a lot of nice stuff in WebGL 2 (eg float textures, vertex textures) but as soon as you try to use it you either sacrifice compatibility on a bunch of devices, or you have to check for various extensions to try to figure out what’s going to work, and try to fall back gracefully if possible.