Because if it's going to be a while I may buy a ps3 with a subscription and just play the free games from there.
Honestly? I bet for a good long time. I kept both of my PS3s and got rid of my 360 and I am pretty thankful I made that move. I wouldn't doubt if PS+ for PS3 continues even past its life cycle. Can you think of a better way to move to almost all profit hardware for a company?
In terms of new content coming out? Probably a couple years. There will still be plenty of PS3 games in 2014 and some in 2015. They may cycle stuff in and out after that but I wouldn't bet on it.
In terms of still being able to play games you downloaded? Probably many years. Authentication servers are not very expensive and PSN will still be up supporting PS4 and the Vita. I would imagine you'll run through the library before they shut down access.
I don't see why someone would think this program would last a year more for PS3. They will only MAKE money off of this and can you imagine Sony being able to push PS3's with the promise of a large instant game collection? Since none of those games are backwards compatible on the PS4 they can sell systems even at $100 for profit and promise the IGC. I don't see how that isn't a win-win.
They'll continue supporting PS3 for at least a year, probably more. Until there is a large back-catalogue of PS4 games, they can't give away too many PS4 games. It'll cost them too much money giving away brand new, just released games. So they're going to continue to push the already established platform, with a large back catalogue to pull games from.