Is it possible to get multi-user support on Android with help from the boot manager? I know that a common problem with Android tablets is that they lack multi-user support. I wonder if there isn't already a solution that allows me to select the user on boot by linking/moving/changing the data partition.

There are boot managers that allow the selection of the (custom) ROM to be loaded, just like Windows/Linux dual-boot. Are there any Apps that allows me to select the data partition/user on boot? Or let me switch the user data on-the-fly without rebooting?
you can use SwitchMe if you have root, which I believe does all you ask