There's only two ways WWE can go with this right now, since they're not doing Orton vs Cena anymore. Here's how I see it;
Option 1 is Ted Dibiase. We all saw that people could actually get behind Ted, and he's playing the troubled tweener role as good as CM Punk was back in the summer. Ted himself hinted that he'd be facing Orton at Wrestlemania, and most people think that Ted should go over Orton. It would give us a new face main eventer. The problem is the Wrestlemania part. Can WWE stretch out this rivalry for 5 or so months? They managed to build up the Hardy vs Hardy feud for a good few months for this year's Wrestlemania. But they can't take that route with Dibiase and Orton. Plus Dibiase needs to turn face in time for the movie release, so they can't make the turn very slow, with him finally snapping some time next year. So it'll be interesting to see how this plays out. But while Dibiase and Orton will be feuding, the feud probably come into full effect till around the Royal Rumble. So it won't be Orton's "next" feud.
Option to is Kofi... Kofi went after Legacy last night during the iron man match. It's great to see this, I was worried WWE wouldn't do anything with Kofi once he lost the US title. If Kofi beats Cody and Ted (with the help of Cena, maybe) over the next few weeks, I don't see why he couldn't go up against Orton at Survivor Series. Obviously Kofi wouldn't go over, but he doesn't need to. If he holds his own against Orton for 18-20 minutes, it'd help him out alot. He's being pushed well, he's started talking, so a high profile feud would be perfect to cap off his ascent to the "next level".