Actually I was proposing that this be handled outside of setting TOS
bits, but I wasn't clear. basically if I own a router from cisco today
i can prioritize my interface traffic using the "priority-list" command.
i select by protocol. Could that concept be built on to give me per
port control over my routing in the future? who knows.
What you're trying to do is basically what TOS does: choose your
outgoing path based on whether the application is most concerned about
delay, throughput, or whatever.
When a host doesn't set any TOS bits, a router could conceivably
then peek into the packet to look at TCP ports as part of computing the next
hop. However, a router that did so would probably still want to leverage
off of the TOS mechanism by using the TCP ports to determine what TOS bits
the host should (according to Host Requirements) have set.