Saw this proposal / paper on another news site this morning and thought it might be worth bringing to the attention of the IET's technical bods, since I know some of them come on here:
Elsevier (Science Direct) - Standardized nomenclature for photovoltaic connectors
It doesn't quite address the issue of defining "MC4 compatibility" and wouldn't take away from the guidance in the PV CoP not to mix-and-match connectors (which is quite reasonable at present). But perhaps a common language would allow a standard or specification to be defined which would eventually lead to it being possible.
Even it it didn't, as the paper suggests, a common and consistent language would reduce the risk of erorrs during installation.