Shenmue 3 would be vastly different than what it originally was for Shenmue 1&2. Shenmue is basically an detective adventure game with slightly different outcomes based on player success, failure, or the process in which the player solves a problem/objective. While I personally loved that type of gameplay and style, it would be a hard sell for any newcomers currently.
Shenmue 3 being made now as a PS4 exclusive could entail a Heavy Rain type of game where there's dialog choices with certain NPC's, instead of questioning any and all NPC's. QTE's would still be a central mechanic during cutscenes, combat would be identical or resemble what was created for Shenmue 1&2.
Basically, more spectacle with characters and character interactions, less interaction and exploration overall, open environments would still be in, less detective work more interrogation or branching conversations, updated but similar combat system.
Shenmue 3 wouldn't be much different from a more open world Heavy Rain with realistic time cycle and fighting game (straight out of VF5) sections added in.
Not that hard a sell, imo... if not for the fact that it would be the third chapter in an unknown series, something not even R* has been able to overcome with Max Payne 3.