Which begs the question, is an additional crew member needed to supervise the ETH/HEP in the Class 73 with a 66, but would a 67 be monitoring the 73's ETH/HEP from the driver's desk?The 73/9s have AAR multiple working fitted so they can run together with 59s, 66s, 67s, and 69s.*
The advantage for the 67s is that unlike the 66s they can provide HEP, so it would be possible for the 67s to run on their own if the couplers and other relevant interfaces were modified. We're probably just going to have to wait and see though.
* = technically the Chiltern 68s too, for completeness