What's my next back? Well if all things were the same as they are now I'd shoot for a 80 megapixel (which is one of the reasons I just switched lenses). I know this sounds fickled. I'm in no hurry what so ever to switch/upgrade backs. I was in need of a new focal length as no matter how much I tried I just didn't love the 35mm as much as I thought I should and used my 72 and 120 more. Hell, to be honest I use the 72 a heck of a lot more than the 120 due to the shot barrel design.
Bottom line (if I were to be totally honest with myself) is that I am really enjoying the IQ160 so much that I simply don't want to change.
I guess my short answer to the "No love for the IQ280" is....
While it looks good - it currently does not make sense to spend the money.
One more thought: the main reason for me to switch to either the IQ180 or 280 is the ability to shoot at ISO 35.