The current implementation verifies that the sock passed is a stream socket. This limitation appears to be arbitrary and is limiting.

* An AF_UNIX SOCK_DGRAM server socket becomes readable when one can accept(2) it. Just like SOCK_STREAM.
* One could provide a different factory to create a reader/writer to use a SOCK_DGRAM socket (but most likely nothing special is needed)
* A connected AF_UNIX SOCK_DGRAM socket will work with normal read/write messages just like SOCK_STREAM.

AF_UNIX, SOCK_DGRAM is interesting because it provides a reliable transport for messages. This avoids having to write message segmentation or packing messages in any kind of envelope.