While I don't think the likelihood is that high, I'd like to point out that people probably said the same thing 15 years ago about Macs...and yet I spend about half my time on my Mac playing games in Windows, so...never say never.
PCs are much different than mobile devices.
Allowing people to install alternate OSes would allow them to break from iOS's "walled garden."
And you still cannot install OSX (at least without some "hacking") on anything but a Mac, due to the software being made for the hardware (just the same as with iOS)
And the main reason Apple made Macs able to install Windows was because most applications (mainly business) are made for Windows; the opposite is true on mobile devices, most things are developed for iOS (although that is rapidly changing)
I just can't see Apple letting you install another OS on an iDevice, there's no real reason, anything on Android is also on iOS, unless Apple doesn't want it there. They want control over your device, and without JBing, they have it.