Gemini pickups make several models with asymmetric splitting, so the split sound isnt weak, but there as still lots of coils that arent paired off with one in another wind, giving single coil character. The poor soundclips put me off them though. Yeah, I know, a million and one other variables, but they really sounded shite.
BK made the knuckledusters, which by all accounts do have humbucker and single tones in one pickup, but the design is very unconventional and not a retrofit for most guitars - they have to be routed especially for them.
I've wired two singles, one RPRW, in series in two guitars - one was the middle and neck, two irish tours. Very interesting, and cool tone with them both on, but it while its humbucking, it doesnt sound like a humbucker, presumably due to the large seperation of the coils. The other was two singles (generic dean stock) that I made into a humbucker and put in a humbucker routing, neck position. Really compressed sounding humbucker tone. I didnt split it.