RNP-4 requires CPDLC (controller pilot data link communications) which is only widely available in airliners. This allows for communications between controllers and pilots and automatic updating of position to controllers when passing waypoints. This eliminates all the HF radio hulabaloo. As far as corporate it is only certified in the BBJ G550 an Falcon 7X that I know of. It will soon become an integral part of Corporate Aviation I imagine. A note on RNP-4: It allows tighter over the water spacing thus more efficient use of routes, (30nm Lateral,30nm Longitudinal). It is only required on some routes near Australia and Maybe South Africa and these routes are depicted with CPDLC on the oceanic charts. Bringing your aircraft up to standards would involve either new equipment with AFM supplement or an STC.