Which begs the question, why hasn't someone tried? It's not like there's no talent out there for such a project.
My personal opinion is regardless of talent, you're going to have a hard time selling it to stations as a syndicated product without one of the major broadcast companies getting behind it. You'd need a company like Entercom, that's shown a willingness to air non conservative styles of talk, to commit to it on a network of stations. Perhaps as late nights on some of their FM talkers in not openly hostile markets, say Kansas City and New Orleans.
A lot of independent owners are so ideologically committed to an all conservative lineup, it's a hard sell. So that's the first challenge once you find the talent and commit the money to it.
There's a left leaning talent from a major New England market with a diverse background including standup comedy. He started in radio doing fill ins in Boston after a show on a college station. He's now one of three voices on a morning show in Chattanooga, TN. There are very few places for talent that doesn't do conservative talk to go on terrestrial radio, regardless of how good they are. Conservatives complain about the "mainstream media" - but in the case of talk radio, they are the mainstream media. Moderate to left leaning voices are a rare exception. Even stations successful with left-leaning talent in the past seem eager to tinker with the formula, case in point KIRO in Seattle, which canned a successful moderate duo in PM drive to bring in a three person show including a very hardline conservative from their all conservative AM station KTTH.