I suspect it is related to the work on User input, i.e. the Joystick based UI. In case the input device only has one button, which would map to "select as target", a binding to interact might be useful.
This change makes WoW playable without a mouse, as interactions were previously the only thing you couldn't do without one. Although "playable" is being very loosely defined :P. It's kinda useful when your mouse dies or you want to play with one hand.
I played FFXI with only my left hand, and I loved it. I'm right-handed.
However, even with these changes I doubt I'll do the same in WoW. The UI is too different (much much better) and doesn't work well with the joystick design that plagued FFXI, IMCO. We'll see, hopefully I'll at least be able to stop using belkin's crummy software and just bind directly to the "real" joystick buttons.