Frankly, I think con #3 on the XPan list is not a worry at all. Order a bunch online. I get mine for $2 a pop. They have a 10 year shelf life. And I don't think they'll be going away any time soon. Lot's of electronics use this kind of battery.
The Xpan is a great compact panoramic camera. If that's the goal, then I'd just keep it. On the other hand, if panoramic is going to just be a every once in a while thing for you and you'd rather have MF, then go for the 6. Though personally, I think I'd get a Mamiya 7 instead - I think the panoramic adapter for the camera gives you negs that are the same size as the M7. And with the 43mm lens, you've got an amazing lens that would put down essentially the same frame as the XPan. But maybe sharper
Also, I never use a grad filter with the 45mm on the Xpan. Maybe I'm just not as sensitive to the vignetting...