I agree! Like 0xfeba pointed out, really annoying things like coinhive could eat all your CPU if no permission was required. Some sort of web API that tells the browser how many threads it can allocate for rendering and code execution. If the thread count exceeds a configured maximum the browser can ask the user for permission.
I don't think it'll go that way, i remember when web workers first came out i wrote a simple raytracer with some GI and optionally used web workers if available for multiple threads. It worked fine until some browser updates later that limited the amount of web workers pages could use (or the amount of time each worker got, i don't remember, it has been a few years) making the web worker version have pretty much the same speed as the regular version.
Out of curiosity, what technologies are you leveraging to write browser-based 3D games? Lightweight WebGL libraries, something higher-level like Unity, or something else entirely?
Rolling my own graphics engine (ugh!) to create a voxel octree platform. Front end uses C++ to Webassembly for the engine core and Typescript for the UX. Backend uses Java with a MSOA. All using a reactive message system.
There is support for efficiently passing data around. You can directly get binary typed arrays from XmlHttpRequest without intermediate processing, and you can pass them around without memory copies to WebWorkers using Transferables.
More recently you have shared typed arrays that work like shared memory between threads (as of Safari 10.1 / Chrome 60, Firefox too)
