I had the same initial reaction. I wanted a tokio UDP server that delegated to other things. Working w/ tokio streams, futures, async (which I understand are all still in beta) was quite challenging to make sure they could all get back to the read/write of the UDP socket. Basically I end up having to split UDP read/write then concat/join disparate streams or use mcsp channels to fan everything out and get it back to a single stream.
