It's not unheard of for hardcore gamers to end up with multiple consoles of the same type. I originally bought a 120 gb slim for my digital content. Then I bought an 80 gb original model from GS so I could play my PS2 games in high def. Not trading in either at the moment since the only PS4 game I'd want to play right now is Pinball Arcade which I only have on PS3, Vita and Android. But it might be a good deal for a more casual gamer who is ready to move on to the next gen. For the record, I also own six Dreamcasts, one of which is a broken kiosk model that I kept for sentimental reasons.
But before you guys get rid of your PS3s, I just want to remind you that Persona 5 is only coming to PS3, which is the best reason to have one ready.