Alright, since you posted that ...

During the morning constitutional, I booked the last parts of WM ... Taker never responds on Raw ... not a peep.

Cena shows up to WM "in the crowd as a fan" ... DB asks him to be his tag partner from in the ring to him out in the crowd (fortunately he's in the front row at that time by pure chance of course) ... Cena gets in and the match doesn't go too long (~10-12 minutes) ... I don't know John's cardio level but I suspect he can still go ... match ends, DB & Cena go over (obviously).

During the celebration, the ring and house lights cut out, blue lights come up(but no bell toiling, just the visual), Cole and the other idiots speculating for 20 seconds, then in an instant the stage and Titantron light up, "Keep Rollin'" fires out of the sound system, and there's the American Badass on his bike at the top of the ramp. No real break between the matches (besides the few minutes' celebration), just morph the two into one long segment essentially. Needless to say the celebration and what would assuredly be a long Taker entrance will give John more than enough time to get his breath back if he needs it (though it's not like it's going to be a Guerrero/Malenko technical masterpiece).

That would be interesting and novel, imo.

Therefore they wouldn't do it .... gotta be sure to waste 4 minutes on a Cena video package throwing a fit about Undertaker)