My problem is you need to pay for the game again. If I could pop in my PS3 version and play for free I wouldn't have this issue but repaying for games I already own is just plain greed.
With the amount of use my PS4 gets it's not worth the money for me.It's a subscription based service, your $10-$20 (guessing) a month allows you to play an entire library of games. So yes a few games you might own, but I'm sure you'll still come out on top.
There will also be renting games on a game-to-game basis (no sub) and you can even purchase full games if you don't want to deal with renting/subscriptions.