Right, well the question is what format holes there are and we can add "but it's unlikely they get filled due to the business". We all have different options for our music and if we want classic
country, blues, political talk, Alternative or whatever there are streaming stations, satellite radio, or even HD radio for those who have one...though Oldies, blues, Irish etc all got take off the HD2s,
as it is.
Greater/Beasley did keep Talk 96.9 going for some 13 years or so but gave up. iHeart is able to do conserv talk on AM at least and the likes of RKO stay alive there.
Some specialty shows are out there. WMEX and WBMS will be doing some individual oldies shows. There are a couple Irish music shows (WROL and WNTN IIRC), and some college or public stations
can bring you shows with jazz, alternative, and so on. Bittner's WJIB does cover some oldies as well as standards, etc.