Imagine, a process per browser tab for all the things! Why should this not be the case? It would be a revolutionary improvement in process visibility, in general. moreover I don't see why there would be any limitations over what you get with ps and dtrace.
Indeed, I suspect there is a quite nice visualization of the kernel itself that would fit nicely in a browser tab. Maybe not a real-time picture, but surely you could do simple simulations at the very least, and perhaps set configuration options if you wanted to change your own kernel.
React Native and NativeScript are exploring different tactics beyond the most limited webviews on Android and iOS systems. Crosswalk and others explore yet another approach for bringing better webviews to such platforms.
At some point too, performance doesn't matter so long as the users are happy. A lot of technical folks notice performance, but most consumers do not. WebView-based application toolkits don't need performance to "win", they just need that sweet spot of developer productivity and user engagement that is much easier to do than you think, with or without "performance".
Given FirefoxOS is also retired and ChromeOS seems to be in the process of being replaced by or merged with Android, I figure the cross-platform toolkits are more likely to win than the browser OSes.