I think they'll make a traditional game console with Dualshock 4 and keep their gimmicks to peripherals. The PS3 didn't have a gimmick and it's still going to take 2nd place even though it launched at an outrageous price, had no great (system selling) games in the first 2 years, launched a year after its primary competitor, was a bitch to program for, and had terrible online at the start.

If they don't put some expensive controller or peripheral in with it and use off the shelf parts then they will have a cheaper and/or more powerful console than the competition, it will have the best first party support with all their studios, and third parties will love it if it has easy to program for PC parts. Sometimes simplicity can go a long way and this would make it so they can market to everyone that considers themselves a "hardcore gamer" and have great success with that crowd. Considering that PS3 didn't really hit mass market, had a basic split with hardcores with xbox, and may still reach 100 million I think they'll be fine with that crowd.

Relative to what r3tr0gam3r1337 said, could the (somewhat) whole catalog of PS2 games available on the PS4 be a big deal? Either as downloads or through streaming?

And will we see the end of the PS2 life-cycle, amazing as it's been?