I disagree with this. If the only surface area of the underlying transport that the implementation uses is Read() and Write(), then it should be an io.Reader and an io.Writer. If it wants to mess around with read/write deadlines, then you'd have to bring in net.Conn, but it doesn't, so don't.

If you're worried about someone using bytes.Buffer as their transport layer, net.Conn doesn't fix that; there is net.Pipe. (It's not buffered, though.)