Console modder Edward Zarick, creator of the portable Xbook One and PS4Book consoles, has finally solved the backward compatibility problem. He has created the new Xbook Duo, a combination Xbox One and Xbox 360. It is also portable, much like his Xbook One, with its own HD 1080p screen.
The Xbook Duo doesn’t utilize different drives or anything like that. It just wires the innards of the two consoles together such that they can use the same hardware. You can switch your consoles from Xbox One mode to Xbox 360 mode with the flip of a switch.
Unfortunately, the Xbook Duo is just a prototype for now and is not yet for sale, like his Xbook One and PS4Books are. It is not yet clear whether or not he will create a similar console combining the PS3 and the PS4.
Source: Edward Zarick