And besides, the Steph-Jericho aliiance wouldn't work out. Lets go with what you said. Steph is scared of Vince, so her a Jericho made an agreement, if Jericho attacks Vince, he gets a title shot. Vince wont see the attack coming by Jericho. And then it's reveal Steph and Jericho were working together. It's a dumb storyline to me but anyway.
There's the matter on when Jericho would get his shot. Wont be at the Rumble because that's already set as Cena/JBL. So so then theirs NWO, it could happen there, but as you said, Steph and Vince would have someone rep. them at Mania. So they would need a build up toward their match. Meaning no title match at NWO. He wouldn't get his title match at Mania because he'd be repping Steph in the match. So the only way he'd get his title match is if he wins at Mania. And if he wins, then that means Steph is the (on-air) owner. Two in a half months is not nearly enough time for a build-up of a match like that, where complete control and ownership changes hands. And wouldn't when Jericho attacks Vince, wouldn't she want him to take him out, injure him, break his ankle, do something so that he doesn't return? The storyline wouldn't work. And when has Mr. McMahon been a face and not suck besides the Invasion storyline?
That's why I say Steph goes as a face, Vince comes back as a heel, he reinstates Jericho, Steph is mad that he does that and that he's trying to take "her show" from her, that she challenges him to a Battle of the Billionaire II. She get's her rep, Jericho is Vince's rep, sounds logical to me.