I wish that people would stop going on about people's investment in EF-S lens when they are considering upgrading. To hog tie yourself to a specific technology is to put a ceiling on what can be achieved – so why limit yourself to APS-C when it is clearly demonstrable that other technologies can deliver more. APS-C is a budget technology nowadays, technology has moved on and as photographers we should always be aiming for the best.
There is pretty much a consensus about the best glass on the body is the way to go. So people wanting to upgrade their bodies will almost certainly already have a collection of non EF-S lens.
How many really top quality ef-s lens are there to really consider?
People upgrade because they want something better than they currently have. What is being discussed in this thread is the IQ improvement, specifically moving from APS-C to APS-H which would give an upgrade path from the current 7D to provide better IQ, better low light performance and higher fps - in other words a super sports body without going down the more expensive (for lens) ff route.
At the moment the lens technology is limiting us, from a budgetary point of view, from delivering a mid-range solution with full frame sensors to get the reach that many want for their photography. As said many times the 1.3 crop APS-H approach is a compromise solution, not the best in anything just very good all round. The 1.3 sensor is much cheaper to produce than ff, so it will be possible to continue for Canon to produce bodies in the price range of the 7D/5DII whilst delivering technological improvements – we already know it would be straight forward for them to deliver high mps sensors (40+)