What if the Xbox 720 was just a "windows box"

And it will be called PS3

 

I think you think they will release the Pro at a later date. In this scenario I envision that they will most likely launch side by side. Since you need the Pro for the tablet and specs have leaked for the tablet already.

Most people will still buy the cheaper Xbox. Game Devs could design the cheaper xbox with 720p in mind and the Pro box with 1080p in mind. They will play the same games and the average consumer will just get the cheaper box. The graphics will be close enough that the average consumer will only get the Pro. They will not advertise them so that only the Pro is appealing. They will make them both seem appealing to consumers.

Especially in the begining of the gen. when Devs are still optimizing their game engines for the new consoles graphics would be close most likely. Additionally, assets for both versions could be stored on the same Blu-Ray since I doubt devs will be using the whole disc at the start of the gen.

This makes sense and I hope MS does follow through with what ramr said.