Pyodide uses its own event loop which just subscribes to the JavaScript event loop. My suspicion is that this will be more efficient than using uvloop since v8's event loop is quite well optimized. It also allows us to await JavaScript thenables from Python and Python awaitables from JavaScript, whereas I would be worried about how this behaves with separate event loops. Also, porting uvloop would probably be hard.

As far as I know uvloop is not supported in Pyodide, mainly because it requires compiling libuv into WebAssembly (which is possible but not trivial).

In any case, it shall be possible to run uvloop fully inside of WebAssembly. However, doing so will prove challenging using their current architecture