Sadly the proliferation of middleboxes means that deploying a new Layer 4 is all but impossible:

* https://en.wikipedia.org/wiki/Datagram_Congestion_Control_Pr...

* https://en.wikipedia.org/wiki/Stream_Control_Transmission_Pr...

Curious to know if things can every move towards a point of allowing things. I know in many firewall 'languages' do have something like "allow tcp/443" or "allow udp/53" for nomenclature: perhaps something like "allow stream/443" and "allow dgram/53" to include (e.g.) TCP/SCTP and UDP/DCCP would allow more flexibility.