Not only this but the problem with online platforming games is lag, in Mario Kart players living far away or players with bad connections resulted in the karts glitching a bit and not getting hit at times. Sometimes players fall off ledges and instantly gets back on the track due to having lost connection for a millisecond or something.
However with a platformer lag plays a much bigger role due to the precision involved when interacting with the world and player 2 while both systems are trying to calculate player positions and other outcome.
The syncing would have to be seamless for the two games to decide and agree what to do in some situations as there are so many possible glitches that can happen if data packets are delayed.
I would like someone to point out a game that accomplishes this, has there been any online 3d platforming games that actually worked in the past? Most online games out there work with a little bit of lag because there's stuff that makes up for it and disturb the game outcome that much. To my knowledge the only practical way of doing online is to have the other players show up as a ghosts, like time trial ghosts, there being no way of interacting with those players and them interacting with stuff in your own stage, meaning that both games doesn't really have to sync flawlessly for it to work.
A way of making a multiplayer Mario online platformer work the way people expect is to have it within a single country and invest in insanely huuuge amounts of money on dedicated servers capable of doing the most important calculations from there instead of having the two systems synced. I don't see a reason to invest in that kind of research for a title like Mario 3D World where it isn't needed, this is a case where it would actually detract from the single player experience due to how much time and money it would cost. People expecting an online feature in their 3D platformers are like people expecting their Wii U to come with a toaster functionality. It's dumb.
