For my example I will use an Electrostar...
I don’t recall the brake cylinder monitoring via the MITRAC from my time driving Cl379s, but I’ll take your word for it. It’s been a few years and the precise details have already faded.
However Electrostars are an unrepresentative example, as a lot of MU trains with EP brakes do not have this feature nor any in-cab warning that a safety system has been isolated elsewhere in the train. There are, therefore, conditions where the train brake may not fail safe (those in the know should know what I’m talking about, as I’m not going to elucidate further on this point).
Obviously there are restrictions in place for moving any train in such degraded circumstances, and this is where Human 1.0 comes into effect. There are procedures on the depot that ensure that everything is done correctly and a train passed fit for service before being released, train prep by drivers and/or depot staff and train handover procedures where crews are relieved en route. All of these things are done for your safety whenever you catch a train.
To apply your MITRAC idea to the Mk5s, you’d be looking at some sort of decentralised computer network with a microprocessor on each car communicating with all the others. It’s not a trivial matter to set this up and then getting it to work with a loco.
Could the Mk5s have been built with an EP brake, controlled either through the jumper cables or a connector block? Yes they could. It’s also possible that the locos could have been provided with translator equipment to translate brake pipe pressure into electrical control signals. But they chose not to, presumably because the existing two-pipe brake technology is sufficiently well understood and well-proven that departing from the established system for loco haulage was not considered justifiable.
Would an EP brake really have conferred much of an advantage? Yes there was an error when forming up this particular train, but there have also been errors when attaching and detaching MUs that have resulted in incidents together with EP brake faults and failures that have affected the braking performance of individual trains (I know because I’ve had one myself). At the risk of yet more repetition, this is where railstaff carrying out the appropriate checks guards against problems becoming incidents.
In this case I rather suspect that, assuming the brake test was carried out before leaving Carstairs, there wouldn't have been an incident if standard air pipes were in use rather than the Dellner couplers. That is because the closure of the isolating cock was presumably accidental
And this is what I’ve been saying for a while now. All the signs are pointing towards this being a process failure rather than a technological failure. Like you, I suspect that the unconventional means of coupling the coaches and making the air connections may have caused some confusion for the ground staff which, together with incorrectly brake-testing the train, caused it to leave Carstairs with the brake pipe isolated between the loco and train. There are no fault conditions that could not have been identified and rectified had the train been correctly brake-tested and, as such, the
appropriate response would be a tightening-up of the procedures to mitigate against a repeat.