The Royal Navy were generally not happy with the NelRod turrets. So there had to be a redesign.Some interesting posts. So, given that going for 18" guns would have been a no, no, both from a treaty point of view, and the development time to design and build it, there was the possibility of a G3/N3 big brother version of the Nelrods. But it seems, experience with them, and a rethink, brought any new design back to a more conventional layout.
The other option that may have occurred, after reading the comments, is that after starting a couple of KGVs, the issue of the 14" gun standard goes away - why not then use up the spare 15" gun turrets i.e. an early Vanguard though maybe not so big - then go Lions!?
The spare 15" turrets would have resulted in a ship that was too long and heavy (more armour for the length) or too lightly armed (6×15 inch guns).