Consider starting as simple as just making the iOS version available on the M Macs. The UI is good enough. Then make the better version. 

Regarding the TNC, anything should be easier to use than direwolf, even if not perfect. Maybe reach out to SDR-Control app dev (I think he's name is Marcus), he might be able to help. He did reverse engineer Icom/yaesu/Ken woods interface to perfection :)