My vote is for the Mamiya 7 with the 35mm panoramic adapter kit, you get all the Mamiya 7 lens changing options as well as having the option of shooting 120 film and 35mm panoramics.
That's what I use and it's AWESOME!
~Stone | Sent w/ iPhone using Tapatalk
That's a good option, but it doesn't really replace the Xpan - the Mamiya 7 is a much bigger camera than an Xpan, and the widest it goes is 43mm, which for all intents and purposes is just as wide as the 45mm "normal" lens for the Xpan. The Xpan does have as an option (albeit a very expensive option) a 30mm wide-angle. AND the Xpan can switch back and forth mid-roll from 24x65mm to 24x35mm frames. It is truly a unique camera.