Who says we want them at all? As previously suggested by some, I'm of the general persuasion that it's a gimmick - for PR or other reasons.
I'd love to hear of a story (good or bad) where this technology has been in use for a number of years already - how it was implemented, at what total cost, what real educational benefits have been realised (if any), how many devices have been replaced and so on. Like
BSF, a potentially good idea conjured up with heads in clouds, but realistically it's just a huge mess that hasn't been thought through properly.