Not going to happen, parents would freak, politicians would freak, they wouldn't see the point, they just won't do it.
Some cadet forces do - Dorset ACF has it's own batch of '98s, and my schools CCF has used paintball markers for CQB exercises in the past which was good fun - this was before BFAs (Blank Firing Attachment) too, so they alternative wasn't even blanks - it wasn't safe to fire them close to someone else (if you don't believe me, search for a video, you're sure to find coke cans and fruit being ripped to **** by blanks) so with markers the cadets could clear a building with flashbangs etc, but rather than just.. not fire, actually hit each other with paintballs.