When I was out at the Mothership to discuss my custom with Susan and Mica, Susan told me that John used an action that was unusable to just about everyone except himself. She told me a story about how they had made an instrument for him, and were going to deliver it to him at a venue not far from the factory. The action was insanely low (and also, his fingerboards on his Alembics were completely flat, no radius), and no one could play it without it buzzing all over the place. Susan told the tech who'd be going with her to deliver it to bring his toolbox just in case.
They got there, took the bass out of the case, handed it John, and he started doing Won't Get Fooled Again. Susan asked if any adjustments were necessary, and he said no, it was fine.
My view is that if one likes action that low, one will have to put up with changes in the weather, humidity, etc. in order to achieve it with a wooden instrument. My guess is action that low is very unforgiving of any number of changes, and I imagine John just felt the effort wasn't worth it. Most of us don't use an action that low, so it isn't as much of an issue for us as it was for John.
I'd love to know what kind of action he used on Fenders, Gibsons, etc. Those instruments, IME, are much more difficult to dial in to low action than Alembics, but that's just me.
Alan
