So a kid with XY plays against a kid with ORAS. The kid with ORAS uses Mega Sceptile, and the kid with XY just looks at it and gets annoyed he can't get it.I believe that approach is actually kind of counter productive, since having a mega you can't get in your game (since mega stones can't be traded, or did I miss something?) smash your team is much better advertising for your game than just not being able to battle certain opponents in my opinion. Had they patched the new megas in, XY people could have battled them, but could not obtain one.
Having something used against you that you can't get isn't good advertising. It's unfair and a very big taunt.