I assume Rollins and Reigns will defend the titles against The Usos at MITB and Ambrose (being the closest thing to a leader of the group, hence the singles title) could enter into the ladder match by himself. What would be the point of all three guys entering into the match? That's basically admitting that they're competing with one another, which doesn't seem to fit into their gimmick at all. Even if they enter into it in a "As long as one of us gets the briefcase..." way, what happens in the hypothetical scenario that everyone else is cleared while just the three of them remain? (Same logic with them not entering into the Rumble match earlier this year.) With just Ambrose alone, I can see it making sense and I can see him winning the briefcase, actually.
I speculated awhile ago that Ambrose's ego could end up playing the biggest role in the demise of The Shield.