Not 100%. 
I think the "user-only" option is very nice if you want to rehabilitate a completely messed up system. Otherwise one would be copying back all the junk that caused the mess in the first place.
I doubt that persists on an installed system after a reboot.
The better systemwide (debian)GUI option is to use "sudo dpkg-reconfigure keyboard-configuration" as already mentioned here: Howto use E16 as your daily desktop - intro first steps
I do not think the time is right for testing e17/e22 yet but that is for Thana to decide.
As long as we're in alpha/beta testing I think that the live-boot shouldn't even offer the option of chosing but go straight into e16....for now.
The user always will have the option to log out and then log into the other DEs. Allowing to chose at first boot just creates expectations which cannot be upheld in a short timeframe.
It makes forum posts messy getting the two (or three) mixed up ...... methinks a separate e17/e22 beta testing howto wiki entry would be good too.
That way e17 lovers can help each other out in creating own modules, fixes and suggestions until @Thanatermesis starts working on it. 
