I really can't see coordination taking account of selected MCP altitude as the way forward.
2 Reasons:
Firstly, there is no certainty that an aircraft will be manoeuvering towards its MCP selected altitude. In fact, when considered in terms of an ATC commanded avoiding action that happens just before an encounter (and lets say just before an RA), it is quite likely not to be the case.
If ATC say 'avoiding action' anyone with a healthy sense of self preservation is going to punch the a/p disconnect and manoeuvre the aircraft, only catching up with the MCP selections later.
Secondly, what you are talking about is effectively a system inhibition against manoevering opposite to the MCP altitude direction. Don't forget, TCAS already has inhibitions built into it for various reasons, and if we add any more we will start to get situations where one (or perhaps both!) aircraft are unable to manouevre in either sense!
I would never claim TCAS is flawless, hence my advice on this and other threads with regards to handling TCAS incidents, however the area that the system can best be improved has got to be crew training IMHO. Searching for a technical solution to what is a training issue is not the way forwards I feel.
CPB