Interesting, but would have obvious drawbacks when it comes to addressing any OS vulnerabilities or improvements - suddenly you have to reinstall ALL your applications!
This reminds me of Nintendo's approach to emulation for their Virtual Console, actually. Rather than having a standalone emulator that you download images for, they package the emulator with the game. This way they never have to worry about inadvertantly breaking anything with a future release, but on the other hand any subsequent emulator improvements do not retroactively apply.
I think you could save and fork OS images. At the same time I would think vulnerabilities wouldn't matter as much, but you are right that it adds complexity to managing a system.
This reminds me of Nintendo's approach to emulation for their Virtual Console, actually. Rather than having a standalone emulator that you download images for, they package the emulator with the game. This way they never have to worry about inadvertantly breaking anything with a future release, but on the other hand any subsequent emulator improvements do not retroactively apply.