I don't want to spoil a good rant but the same rule WAS introduced at the same time for Part 27 Cat A rotorcraft and has been sucessfully applied to MD900, EC135 etc.
Brian A is right that the issue has been covered extensively elsewhere.
Lets just say, there is a rule, the aircraft was certified, and as long as the heat exchanger and its pipework are the source of the leak, IF you follow the RFM action to activate the bypass in seconds AND watch the oil pressure like a hawk until it stabalises then you have time to seek a landing site. So far there have been no leaks from the external part of the system (GOOD!). There have been pump drive failures that have created similar symptoms and resulted in premature landings.
If the leak is from elsewhere then, unlike other types certified to 27/29.927, you will see the pressure drop below 5psi and you must Land Immediately. Leaks from the MGRB itself were claimed to be 'Extremely Remote' but have happened twice to date, about 1 every 100k hours (BAD). The outcome of failing to do that promptly is demonstrated by C-GZCH.
I'm sure those who voiced doubts about the certification 5 years ago will take no comfort that their worst fears have come true.
We can only hope the TSB get to the bottom of why this was allowed.