Well imo they really should be starting a WoW ex pak AND D3 at the same time. I give WoW 3 - 4 years before it really starts to deaden. So if you go by that they could have one more expak in about 1.5-2 years to keep the game limping on with hard core players. Meanwhile they could start their 3-4 year production of D3 which will come out right when WoW no longer has that great of player base and BOOM! Tough actin tinactin, 5-10 mil people back to blizz again.