Of all the suggestions I've read in this thread so far the only one I really think would work would be John Hodgeman.
I think this situation reflects on one of the core problems of MSNBC and left leaning news outlets in general. The exact core target audience for the majority of liberal or more left leaning news is the demographic who has little to no interest in watching actual news programming unless it's either funny, "ironic", satirical or trying to be some combination of the three. While the more conservative leaning demographics still use/enjoy the traditional style news outlets (news shows/channels) and that's why you have Fox News slaughtering MSNBC in ratings. Maybe they need to talk the likes of Stewart, Colbert, etc into simply taking over MSNBC. Or if you wanted to go CNN and try to angle for the middle ground pair them up with conservatives like Dennis Miller. But I could be rambling.