Given the data available from the NG fleet I could see a rewiring mandated for the next C or D-Check. It shouldn't be too much of a hassle, especially in the later case.
However delivering planes and issuing CoA to already manufactured but non-conforming planes ... that's a horse of different color, especially in today's regulatory atmosphere.
I guess we are seeing one of the risks in stockpiling not deliverable planes materializing. If only anybody had warned them.
They'd better save themselves a lot of time and money and start fixing them NOW.