I will go with a wild guess and say in Summer of 2016. 

What are your guesses?

FM5 has the advantage of being a Launch game so it could take a while. FM6 is better in every conceivable way so hopefully that'll make it outsell it quickly.

Hopefully never, that way MS realizes Forza is dead at this point and concentrate efforts and money into reviving their best racing franchise: Project Gotham Racing.

With a guest star of the Batmobile.

I doubt that Forza 6 will outsell Forza 5.

First thing first. Forza needs to have a bigger launch than the Forza Horizon 2. Next week we will have some kind of indication. It should get some help from the bundle for sure. They run the risk of milking Forza dry.

There are chances but I don't know...

Even so Forza 5 in this site looks suspicious... so I will stay off this comparison.

shortly after they bundle it. and by shortly i of course mean most of a year later as FM5 sold over 2 million.

It wont.

Sadly, Bizarre creations has long closed its doors.

I would like to see it revived aswell.