Dan Rather is a terrible idea for MSNBC at 10 p.m., and I also don't understand a few of the names on this poll. Lou Dobbs, Van Susteren and Shuster? They already have shows, and Dobbs is arguably one of the biggest asshats on cable news.
I really think it has to be Sam Seder. Stephanie Miller or Arianna would also be interesting, but Stephanie would probably have to quit her radio show and that would suck. Michael Moore might work, but only if it were his old TV Nation / Awful Truth format -- but those were weekly shows and it's questionable whether he could sustain that level of production on a nightly basis.
Here are two dark horse candidates that aren't on the list: Cenk Uygur or Roy Sekoff. Cenk has a built-in fanbase on both the radio and YouTube as well as an established format. Roy is not only big-time connected in the blogotubes (he is the Huffington Post), but he worked on the aforementioned Michael Moore shows, and he has some name recognition with the MSNBC audience.
Who else? Thom Hartmann? Randi Rhodes? Ari Melber?