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I would LOVE for this to happen. IMO these 2 wrestlers put on the best matches in the WWE right now on their own. When theyr'e together in the ring they always put on 5 star matches and for them to do it again at the big one would be phenomenal. I agree neither should be in MITB, as theres enough young deserving wrestlers for that.
If they have a bout at WM27 I doubt it would just be about a rivalry, so if it were to happen the logical thing to do would be to book the match as a unification match of the IS and US titles. I don't want to see that though because WWE needs 2 midcard titles, 1 for each show.
It should be booked as a battle for brand supremacy match like Umaga vs Batista at WM24. This way the titles don't have to be unified and it the bout would some logicity behind it. The match would steal the show besides The Undertaker vs ?