I think the main problem would actually be the added storage consumption of hauling around old iOS system images, as would probably be necessary to keep the mai

I think the main problem would actually be the added storage consumption of hauling around old iOS system images, as would probably be necessary to keep the mainline version of iOS unencumbered from the constraints placed by backwards compatibility — it’d probably just be virtualizing old versions of iOS similar to how Mac OS 9 was virtualized in the early days of OS X.