5 strings on a P or J look soooo wrong!
That's exactly the perception that Fender is up against.
Doesn't seem to hurt boutique makers like Sadowsky or Lull, but they aren't competing across the whole market like Fender, and their customers aren't diehard traditionalists or they would have bought Fender in the first place.
The other point to remember is that 5-string sales are nowhere near as big as you might think from reading online bass forums. According to John Hall at Rickenbacker last year at another forum, one of the music trades magazines published a list of top selling instruments and not one of the top 10 selling basses was a 5-string.