I'm not sure how this would help the lack of backwards compatibility. Most people want backwards compatibility so they can sell their old system, buy the new one and keep playing their old games along with a few new ones while they wait for the next gen to really get going.
Packing in a PS3 version with the PS4 version of a game doesn't make much sense to me. If you only have a PS4 you have no need of the PS3 version. If you only have a PS3 you'll most likely play the PS3 version and not need the PS4 version when you do get around to buying a PS4. If you do have both a PS3 and a PS4 you'll still only need one version of the game and I think it's safe to assume you'll play the PS4 version and toss the PS3 version.
I really only see companies losing money on PS3/PS4 packs. I don't even think it would help PS4 sales. Collecting PS4 versions of PS3 games that you have already played isn't going to convince anyone to buy a PS4.
I do see what you're going for. You're basically making PS3 game purchases compatible with PS4 by way of a second disc. I just don't think it would do anything but lose money for publishers.
