I agree that the 4+1 was the way to go on the JB-5. A 3+2 would just look out of place. When I first saw G&Ls about 15 years ago, I wasn't too fond of the 3+2 on the 5'ers, but they've grown on me. Also, I don't mean to make all 5'ers 4+1, just make it an option along with the wider nut that the JB-5 has. The 5'ers haven't really had any options as they only come with the #10 neck. Maybe time to change it up a bit?
This kind of thing requires more thought. As it is, we have quite a lot of options, and we'd have to do some engineering which would have to be put in the queue and maybe displace something else we'd want to do first... the JB-5 neck is different at the heel than the others.