Buy the digital edition right now, you will get a "free" upgrade to PS4 edition as well. Make sure to grab it before it expires in Jan. You don't have to buy a PS4, just as long as you've checked it out, you should be able to download it later (if/when you get a PS4)
Just popped into Sainsbury's, realised it's out on the PS3. Maybe I won't sell it after all. Shooter with RPG elements? In.