I sent a mail to the tech support team of backwards compatibility and I got replied by a developer. Here is what he said. I asked him that why did they added Rallisport Challenge that was older and not Midtown Madness 3.
We are trying to get all games working. While getting
popular games working (like Doom 3 and Lego Star Wars) sometimes other
less-popular games (like Rally Sport Challenge) just happen to start working
too. We didn't explicitly try to get Rally Sport Challenge
working.
We are working on Midtown Madness 3.
And in the next mail I asked him if he didn't knew of a future MM release and when will they make MM3 compatible with X360.
I'm one of the developers. I'm not an official tech support person. :)
I just like to see the customer questions and answer as many as I can.
We don't have any firm dates yet. We are just trying to get as many good games as fast as possible.
Hope that this helps.