I am thinking of getting a PSplus subscription. What I currently have is a PS3 but in the future I will buy (sometime) a PS4. Will the games that I acquire now from my subscription on PS4 redeemable if I get the PS4 a lot later? (as long as still pay for the subscription of course)
You can't transfer a PS Plus account, because your subscription is for your whole account, regardless of which platforms you're actually using.
As long as you claim the games, you should be able to download them later as they will be added to your download list. You have to actively claim them though, it doesn't happen automatically. The PS4 games will probably not show up in the store on your PS3, but you can log in at https://store.sonyentertainmentnetwork.com/ and claim them from there, which means adding them to the basket as free and proceed to checkout, as if you were buying them.