Lets imagine that Microsofts becomes extremley sucessful with the Backwards Compatibility programm on the Xbox One. In a way that Sony has to react more than just PSnow which isnt even out yet in most of the world. Lets say they answer with a special PS4 Cell Model, basicley they put the PS3 CPU into the new PS4 as well as the 256mb XDR DRAM.

For the GPU the Jaguar APU would be used and the 8 GB GDDR5 ram for the PS3s 256 mb DDR3 ram (i think it would be easily to emulate the rest as the RSX is just an Nvidia GT 7800).

- The Price would be 450$ for this model as a standard PS4 would be 350$ at this point in time.

This new PS4 model would have 3 major features

- the PS4 Cell model would be 100% Backwards Compatible with all PS3 games. You could also stream and record footage and the PS3 games would run even better on this PS4 model dueto the Jaguar GPU being more powerfull than the RSX.

- the PS4 Cell could record gameplay footage up to 1 Hour and the quality would also be better. Cell PCIe cards were even sold for rendering Videos on PC back then which a lot of people dont know.

- and third, the extra Cell CPU would be used to improve some PS4 games. It would be similiar what Nvidia is doing by making exclusive deals with devolopers and adding effects being only possible on their hardware which was first called Physx and now Gameworks by Nvidia.

Sony could add extra graphics effects on their exclusives and third party agmes with making deals with them, they have quite the devolopers who could do that. For example the recentley released Batman AC has exclusive Nvidia graphics effects showing how it could look like on a PS4 Cell model.

Sony could do something similliar for a PS4 Cell model. And unlike with Nvidia it would be more justified dueto completley different Architecture of the Cell which PC and Xbox One wouldnt have.

No, I have a PS3 and as long as it doesn't break i'm never going to get rid of it
At some point i realized getting rid of old platforms was a mistake and never did it again

Your idea wouldn't work out for myriads of unlisted reasons ...

Yes i would buy it an a heartbreath

I have a 80 GB fully BC PS3 so no I wouldn't.

No. I have no issue playing PS3 game son my PS3 and PS4 games on my PS4.

how ?

Try Tekken Tag Tournie 1 in that badboy :) see just how fully BC it isn't.

On Topic tho, you can get a PS3 now in 2nd hand stores for 90euros or so, I really don't think Sony should be looking at spending R&D dollars on trying to make PS3 games work in it natively, with the complexity of the PS3's innards it would be a massive effort for little reward, I'd say most PS4 fans would rather Sony sink their time and energies into making future games look nicer.

Tempting... I could see this idea working.
It would be like getting a PS3 extra on each PS4 sale, for just 100$.
The game library the PS3 had, that would be a boon.

That could be pretty cool. I don't really like the price difference though.