Yep. We could have a system like how there's a global system allocator, but you can override it if you want in your app.

We could have something similar for a global async executor which can be overridden. Or maybe you launch your own executor at startup and register it with std, but after that almost all async spawn calls go through std.

And std should have a decent default executor, so if you don't care to customise it, everything should just work out of the box.