I get it...javascript is the universal language. It's also universally hard to fully understand, hard to scale to large codebases, has no shared memory parallelism, has a GC-heavy runtime, and is extremely hard to optimize for performance (both by humans and by compiler optimizers).
I appreciate what React has done, it's pretty impressive. But I can't help but think we're getting into parody territory here.
"Hard to scale large codebases" isn't really an argument, large code bases are hard in every language, JS isn't really an exception here.
Low level stuff (GC, perf, memory) has been, and will continue to be a problem for Javascript. You can mitigate a lot of the problems with well designed code. React attempts to minimize a lot of those problems with solutions that work for most general use cases (and now with Fiber, we're getting even more granular control.)
Until React moves to Web Assembly you're always going to have overhead when using JS. But let me know when you've got a solution for VR in a web browser that's not JS and I'll give it a try.
I happen to think though that the web is an obvious use case for the React model, and phone UIs are only slightly less obvious low hanging fruit that has worked out really well.
The scalability of the model, however, depends on how much workload you can offload into the React system, and with VR, there is only so much you can do. Even if React is handling all of the rendering with extremely efficient native code, you still have to have a your own full 3d timespace model with realtime response demands. Maybe it will work for extremely basic use cases, but at some point having a familiar language becomes a relatively tiny benefit when compared to an efficient runtime.
Maybe this is true, but I'd hazard a guess that most developers are not web developers. [1]
Most of us aren't questioning how VR can be done in a browser, but stopping to ask why.
[1]: http://githut.info/
Seriously, its a lot better now, and if there's a thing you don't like about it (like static typing maybe?) there's something for you out there (typescript, clojurescript, elm, etc...)
Maybe someday this will be better with WASM, but it's not there today. Javascript runtimes work fine (not perfect, but passable) for page-based and widget-based UIs. There's no way I would touch it for something as computation-intensive as real-time 3D modeling.
I think if programming language designers should have learned anything in the past 50 years, it should be, "It's the distribution!"