I think Taker will choose his WM opponents from now on. I remember in one interview he said if anyone would beat him it should be Kane... but not sure about that these days.
Cena vs Taker at Mania has massive match appeal and could well be his final Mania match. All the other current big names have had their shot!
Possibility of HBK/Taker III will always be talked about. They seem to be in massive name territory these days with Taker at Mania, which will probably rule out the likes of Barrett, Ziggler, Del Rio and Miz for next years Mania.
I hope they don't try an Orton or HHH match again. New challengers is the answer i say. Taker could make a career every Mania from this point on, even with Taker winning. The younger guys must be dreaming of that kind of match!