Hopefully never and instead it was canceled so they could make a real Mario & Sonic game already.

Never gonna happen, the foundation of Mario and Sonic couldn't be further apart. Mario in a Sonic world would mean Mario not playing like Mario and Sonic in a Mario world would mean Sonic  not being Sonic. 

Get your DS out and play the first level of NSMB and then Sonic Rush and then imagine both character switching places in those levels. Sonic would break Mario's world in half. 

Looks decent. And visually it could pass as a Vita game... nice work there. I won't be getting it even living in Rio, but if they do a good version of the next olympic games on the NX I'm all in! I had quite some fun with the original Wii game with a friend.

So, are they going to have a game that lets you play as the people who live in the cities that are ruined by the Olympics? Or maybe as the workers living like slaves to build the facilities?

Sonic games are no stranger to having multiple different playstyles within them. The reason it probably (never is too strong) wont happen is laziness and content with how the Olympic series is going, but I'll still hope!