As much as I hate the technical side of webgl (sandbox overhead on top of a legacy API that doesnt even expose 3 generations old capabilities like MRT, webgl 2.0 is far away) it does have a huge advantage of being 0 install no friction access for the user.
I just compile my native code to OpenGL ES and add HTML WebView on top - mobile has a fine app delivery system - desktop not so much and it can handle the performance dip.
It also makes the GUI development faster because most of the UI is simple enough and lets the artists prototype stuff easily with tools they know how to use (CSS&HTML)
I think you got it the other way around. My <insert computer illiterate relative> is never going to dare to install anything native. But she can now use apps that require 3D thanks to WebGL.
WebGL is not where the geek cool factor is, at least not yet. Native might be, isn't that why those $500 graphics cards sell? WebGL brings 3D to the non-geeks.
First, Unity already can do it.
Second, I am not impressed with WebGL vs what native offers, other than geek cool factor.