Late Night?
So Michelle Trachtenberg's tweet last night https://twitter.com/RealMichelleT/status/452275990819913728 jokingly referred to replacing David Letterman on the Late Show, but I actually think she'd make a potentially good surprise selection.
She is both quick-witted and careful not to offend, qualities that would make her a good interviewer. If the high ratings type Kardashian or Lohan personalities were going to appear somewhere, they'd go to her first, I'd assume. And when Michelle did appear on Conan a few years back I thought she was hilarious.
Granted, I have no idea how she'd handle the pre-guest part of the show, and I'd be surprised if CBS went with an out-of-nowhere selection anyway, but they could do far worse than Ms Trachtenberg.