Hi all,
it seems like there is some work in the kernel network stack to have a generic multiplexor/demultiplexor for protocols that implement message-based semantics over TCP: http://thread.gmane.org/gmane.linux.network/378365
They don't implement a specific messaging protocol, but the userspace program can BPF to let the kernel muxer know how to find the length of the message.
This seems like conceptually it is suitable for actually implementing an IPA multiplex inside the kernel and then get e.g. Abis OML and RSL on different sockets.
Not that we urgently need anything like this, but I just wanted to point it out, in case somebody is interestd in it.