There's a couple of famous moving pickup basses. The Gibson Grabber is probably the most prominent since it's been played by a number of famous players (Gene Simmons, Mike Dirnt). The pickup on that one moves a little less than 6. You can hear a difference, but it's not much.
There was a Dan Armstrong bass in the 70's that had a pickup that slid over a long range, basically from the neck to the bridge. I've never seen one of these in person.
There was a Westone headless bass called The Rail which was sort of in the Steinberger groove, but in addition to not having a headstock, most of the body on the Rail wasn't there either. The parts of the body closest and farthest from the neck were still there, but the middle was gone, replaced by a set of steel rails that also held the pickup.
Another notable moving pickup bass was closely related to Alembic. After Rick Turner parted ways with Alembic he put out a line of Turner instruments in the early 80's. This included one- and two-pickup guitars and basses, with an unusual lute-style body. You know the guitar, because it's the famous instrument that Lindsey Buckingham plays, which is now known as the Model One (back then, it was just a Turner guitar since there weren't any other models, just like the original Series basses weren't called Series, because there wasn't anything else). On these instruments, the neck pickup is mounted in a black ring that's positioned where the soundhole would be on an acoustic guitar. The ring can rotate and it actually makes quite a difference in the tone. There were only a handful of basses made in the original run (around 11), and I happen to have 3 of them. They're really interesting instruments.
David Fung
