I don't think Y2J will go straight into the WWE title picture. I'm not sure who his first rivalry will be with, but I would love to see another Jericho/HBK match, preferably at Mania so I can see it live.
There match at Mania 19 was awesome.
I think the plan as of now is to keep the title on Orton till Mania 24 where he'll be wrestling...well take a wild guess...Vince's favourite boy...Triple H. I hope the plan changes though, I want something different than Triple H fighting in the main event at another Mania.
I know it's quite a while away but here are the top matches I want to see at Mania:
Edge vs The Undertaker (World Title vs Undefeated steak, Edge also is undeafted by pinfall or submission at Mania, so this one would be great)
Chris Jericho vs Shawn Michaels (as I've already explained)
Randy Orton vs Mr Kennedy (for the WWE title, that will never happen though, Vince would never put two heels in the main event)
And another Money In The Bank match of course.