This. I like Jazz basses and the sound they make, but don't get on with the piddling pencil-necks. So a Jazz with a P neck would make perfect sense. In fact, as soon as I get some more bass tokens, my bitsa Jazz will be sporting a lovely Northwest Guitars P Neck. So there.
Northwest tell me that their P neck is only an ounce or two heavier than their J neck and the heel width isn't an issue, so...
PS: It's still going to be sporting a Fender J decal... you know, just for geometry, balance... and any other crap I can make up.