What would it take to make an iPad support multiple user accounts?

One place to look might be at dual booting an iPhone with Android.

Update: iUsers for iPad now makes this possible. Check out the video.

iOS caters to both the iPhone and the iPad. Multi-user support on the iPhone would be superfluous. Multi-user support on the iPad but not on the iPhone would imply considerable fragmentation of the iOS platform.

If Apple really wanted to include multi-user support in iOS, partitioning the flash storage and installing several instances of iOS would not be the proper way to go about it. Multi-user support should be accomplished with one instance of iOS and different folders constituting different users' home directories, as is the case with major desktop operating systems. Then user permissions are to be implemented so that one user cannot view another user's files or folders, and thus cannot not read that user's email, etc.

Though multi-user support can be properly implemented on the iPad, it is uncalled for as "portable devices" are often "personal devices".

No non-jailbroken iOS device (publicly) supports multiple accounts, even if one could partition the storage. I have no experience with jailbroken devices so I can't speak to that scenario.

I've seen multiple blog entries lamenting the lack of a feature to lock certain types of content (and they even offered up a couple interesting solutions, too).

iOS itself supports multiple user accounts, but SpringBoard doesn't support them, as it's tied heavily to the mobile user. Some people have put together mods that allow you to add more accounts for the UI/SpringBoard if you're jailbroken, but support for the ones I can find have dissipated.