Everyone is expecting Android O to be Oreo.
This is partly due to O not being a popular letter for starting dessert names.
But the other issue is that Oreo will be a very expensive name. Kraft, the owner of the Oreo brand, will want to make a lot of money out of Oreo being used in this way.
So there is a lot of motivation for Google to think of some other name. Using the name Oreo wont be much help to Android. And the previous attempt at corporate cooperation with KitKat was quite lame.
Using Oreo will likely be just as lame.
I advise Google to just give up on desserts. Use fish instead.