That would create big headaches with existing apps though, which is worth it for major improvements in resolution (e.g. the Retina display) but probably not for more minor improvements in resolution.

Also, the scaling would be awkward, because it isn't a multiple.

Breaking or blackboxing every single application in the process?

I don't think so, that's not how Jobs leads Apple. If you didn't see the iPhone's resolution change until the doubling in the iPhone 4, you won't see any different on the iPad.