I remember waiting for WoW's launch after the second stress test. The wait is blizz-like, the server crashes will be blizz-like, and it'll all be mad fun. Not sure what some other people were playing, but Vanilla WoW is a WAITING GAME.
Besides, the old PVP and PVE servers will tank the technical issues, by the time Elysium starts I believe there will be less problems, less-massive pop than if it launched at the same time.