[gguruusa]

Of course it's possible, just not very pointful - easier to keep both images on SD and flash between them when you want to switch. Fundamentally, multi-boot selectors work by directing the bootstrap process among different partitions. ROMs have their code arranged neatly in partitions, so the same concept would conceivably work. Unlike your PC (which has near limitless hard drive space) phone's have relatively tiny flash space - so the gain would come with a lot of pain. Conceivably you could boot from SD, but that would be even more of a departure from existing code.