The rumours of a next-gen Grand Theft Auto V have been circulating for a very long time as has rumours of a PC version. These rumours are unlikely to die down as German Amazon listed GTA V for PS4 along with what locks like a mock-up packshot for the game. It's not uncommon that retailers are informed about new SKUs before they're announced in order to prepare the database for pre-orders and the likes and it is unlikely, however not impossible, that Amazon would have put up the entry without some kind of official notice from Rockstar.
Update: And now there's an Xbox One version listed as well. Something seems to be in the works.