The service would have to make itself pay off those going to meetings etc. in Cork and one-off journeys as the 2016 census doesn't indicate any significant commuting to Cork from Charleville, Tipperary Town (for Limerick Junction) or Thurles by any means. There is a little from Limerick. Mallow would be the largest contributor, but it already has a decent commuter service.
With that in mind, possibly a Monday morning only service for students and workers heading back for the week is the place to start, with that giving some idea of demand.
What the census suggested was that getting the 05:55 ex Tralee to run on a Monday and to stop in Banteer on other days would be the most effective thing in terms of North Cork commuting. Numbers commuting from Killarney are decent, while Banteer, Lyre, and Kanturk and Cork add up to something significant.