If Season 4 finishes on PS3, I'll probably buy it. But by the time Season 5 appears on PS3, I'll probably have a PS4. So I'll start on that console. Whether I rebuy the old seasons on PS4, I'll decide closer to the time.
I'm already arranging plans to get a PS4 because since the other season 4 tables got released to that console I feel that they may concentrate on that console other than the PS3.