I believe EU will be successful. I hope it will be successful.Potter is not Nintendo/Mario... I don't believe I said it would "ruin" WDW.. Universal will never be a destination for a segment of Disney guests for whatever reason. Universal is in a position to become the primary destination for many, aside from very sheltered Disney guests.. Heck some WDW guests swear they will never go to DL.. Universal will never take catch up to WDW but their goal is to take more people away from Disney for more days and they will absolutely accomplish this with the new park and they may even take away 3-4 days of that weeks vacation.
But I just don't see it making a significant dent in WDW's attendance.