I like the concept, but there are a few ?s I'd throw out there that would probably make it hart to implement and/or confusing.

• Do you only allow it for upgrades to A, C, D, J, R, Y, Z or to any fare (ie 50% to 100% EQM fares)?
• Only for the same exact itinerary, right?
• Do you keep the original restrictions on the non-refundable fare?

I'd much rather see CO focus their programming efforts on things like elite standby than on this, so that would cause me to suggest it be a lower priority on the web site, but I do agree that people deciding to give CO more money should be received in a more welcome manner by CO. I wonder if the third point above (the original restrictions) would make it very hard to implement this, though they seem to be able to do that with the change fee bit, so it shouldn't be too difficult.