The problem with this suit is that it could be the litigation equivalent of bringing back the Fairness Doctrine.
Radio stations use public airwaves on licenses granted by the FCC. If broadcasting conservative hosts only is found to be an improper use of the license, it could have a very debilitating effect on the medium.
Still, I am not sure what relief is being sought and that could be a big thing. If it is money damages, in all likelihood this suit will do down in flames (after all the man could have easily changed the channel). But if it is some type of declaratory or injunctive relief (i.e. the radio station can't broadcast all Republican all the time) then we get into a different territory.
What about free speech/press you may ask? Well, there are at least theoretical limitations on that speech when you are using a publicly granted license. Whether those hold up is a nother matter.