[Someone]

"As for the glue itself, I imagine it's trivially removable by qualified techs (there's probably a solvent that brings it right up?)"

iFixit even mentions their product for doing that using heat for the iPad: http://www.ifixit.com/Tools/iOpener/IF145-198.

Will that work for the iPhone 5? My guess would be "yes". If not, someone will have to find another solution (I guess this knowledge leaks from Apple's repair technicians). I would try cold before I started messing with chemicals.

If it turns out to be not that hard to remove the battery, once you know how, the root of the complaint is "Apple does not tell us how to take apart their stuff, and puts stuff together really tight." The latter is one of the reasons people buy Apple stuff; the former is not something Apple is unique in.