I think the best option here would be for The Undertaker to be Jericho's partner if he's recovered from his injury, because of the amount of bulid up, it's gonna be a disappointment if it turns out to be Kane, The Miz, Brian Kendrick, Dolph Ziggler, etc. And unless it's someone like 'Taker, HBK, Christian or Orton then it'll be a let down.
I'd have Legacy come out first, get on the mic and say "it doesn't matter about who your partner is Jericho because there's not a man alive who can stop us". Jericho can then come out and say "maybe your right, maybe there isn't a man alive who can stop you, but you didn't say anything about a Deadman"
Out comes Taker. Place erupts. Legacy are looking on in disbelieve outside the ring. Jericho gets on the mic again, "you people disgust me, when I came out here you booed me, and now because one of your heroes is my tag team partner, a man who comes from the depths of hell, someone who is unspeakably evil, now you decide to cheer me. It just goes to show what hypocrits you people are" Jericho goes on about saying how smart he is for a bit, turns round and is given, a chokeslam, followed by a tombstone by The Undertaker who then leaves the ring. Then legacy crawl in and get the easy victory.
This would obviously lead to an Undertaker-Y2J feud. As for Legacy, I think they should then get involved in the main event and cost HHH. Then the next night on Raw, HHH can attack Rhodes and Dibase when they're in a tag match. The week after they could do a handicap match where it looks like they're gonna finish HHH for good but HBK runs in and makes the save setting up DX vs. Priceless at Summerslam. If Cody and Ted are allowed to look competitive against Shawn and Triple H, or as their equals, it will work wonders for them.