Sure, but imagine a world where you could run a JVM (just as an example please don't focus on that lol) on your phone (and yes I know Android is JVM-esque, but you aren't just running JVM code on there willy nilly due to the way it's designed). There is no longer an Android vs iOS in that case with respect to JVM and even desktop or laptop applications. Of course there would need to be work done on the development side to deal with screen size and all that fun stuff, but these are all solvable problems and things you already have to deal with. QT has very easy to use Python bindings if you want an easy entry to that so that's no big deal. I don't write a lot of GUI code so I don't know the landscape that well, but I've had success with PyQt6 and Kotlin + JavaFX.

Anyway that's all kinda besides the point. We know how to build VMs; we've done it plenty of times. There is nothing magic about JavaScript; it's just a VM. Are browsers incredibly complex and well designed programs? Yes, but they're not special and their role as the backbone of everything doesn't seem inevitable or wise to me.