Put a small divider between the two, get some quality tape, tape them together. Get a decent Plastic casing, preferably custom molded. Encase the PS4 and PS3 in it. Engrave PS3+4 or something cooler on the custom casing. You're all set!!!
That's it. I will build a PS7 before Sony even gets the idea for it!
Imperator Danknovaxperaux Divi filius Imp XIII Pont Max Trib Pot XLIX Cos CXVI Primus Signiferi Box-xy Princeps Moderatores Pater Forum
Hey Dopplegangergang, you may be interested in this camera phone as well:
On the subject of PS4/BC, unfotunately I don't think this would be a solution - the PS3 (all models) is not flat on top and another system would just slide off. The PS2 would work better for BC, since both models of PS2 were flat .