Mario & Sonic Platformer

I've always wondered why Sega and Nintendo hasn't made a collaboration game using Sonic and Mario, and I'm not referring to the Olympic games saga. They could make a platformer game starring Sonic and Mario. I personally believe that they'd have to make a new world or some type of fusion thing in order for this to work. The chaos emeralds could play a role as well as the power stars. Eggman and Bowser could have created something that fuses the worlds together and each hero side must work together to stop them. Well what would be a good way to go about a Mario and Sonic Platformer?

Yea I think a new world would have to be created. As someone from Nintendo stated, you can't just throw one in another's world because they are two totally different worlds. It could be like Super Smash Bros Brawl, where they create an entire new "fusion" world with all the characters. The Dr Eggman and Bowser collaboration scheme is a good idea too.