The whole idea around this thing is that Ice Climbers would be exclusive to the new 3DS because the increased power allows them to run on the system properly.
So people wouldn't be allowed to play against others using ice climbers due to the fact that their system can't actually support the character.
That said, all the AI calculations should be done client side and sent to the server, back to the other player, so surely the fact that those calculations that make it too intensive aren't being calculated would mean it would be fine?
Idk, this is a silly conversation honestly.
Ice Climbers are obviously going to be WiiU exclusive!