Like others have already said, I don't expect Orton to have the WWE Championship MITB briefcase for very long. If the various reports are correct, WWE MIGHT have Orton cash in after the WWE Championship match between Bryan & Cena. Like most, I'm thinking it'll be a long, physical match in which each hits the other with everything they've got. If WWE wants to turn Orton heel, then having him cash in on Bryan IF Bryan beats Cena for the title is an ideal way to go about it. Nobody's hotter in wrestling than Bryan is right now, people WANT to cheer for him and they go nuts for him. Orton screwing Bryan over immediately after the biggest victory of his career would almost certainly generate intense & instant heat for him. If it results in Bryan ultimately getting a strong run with the title and becoming a bigger star in the long run, then I'm for it.
If Cena retains and Orton cashes in, I don't think it'll have as much of an impact as it would have if he'd cashed in against Bryan. After all, we've seen John Cena in that situation several times already. John Cena has been king of the mountain many times, but this would be Bryan's very first time holding THE top championship. As I alluded to, Bryan beating Cena would be a monumental moment for him. So having Orton show up to, probably, take it away after just achieving glory would make people want to see Orton truly get his ass kicked. Everyone can empathize with the sense of frustration caused by coming within an eyelash of accomplishing a major personal win or, even worse, to attain that personal win only to watch it disintegrate almost immediately afterward.
Part of me would like to see Orton some how screwed out of his attempted screwjob of Bryan or Cena in in which Orton winds up getting pinned via a quick roll up or something after Bryan or Cena provides some sort of distraction. That could also be used to facilitate Orton's heel turn, though it wouldn't have nearly the same impact of Orton screwing Bryan over. As a result, I look for Bryan to win the title only to drop it to Orton almost immediately after.
So yeah, I doubt Orton will be holding onto the briefcase long enough to feud with anyone over it. Also, there's already one briefcase feud going, so another one would strike me as a bit lazy. In the case of Rhodes & Sandow, neither of them are on Orton's level. The fact that neither of them has a ton of momentum going for them, and really haven't for several months, so that puts them on equal footing and leaves the question of who ultimately winds up with the case much more uncertain. There'd hardly be anyone on the roster who could generate that with Orton, and the few that could probably wouldn't generate all that much excitement because it's probably someone we've seen Orton go against many times already.