I've tried multiplayer with 2 players, locally (PC's in same room) and remotely, in both campaign and Horde modes. Bullet cam has not worked in either configuration.
The only time I saw the functionality 'work' was when I (hosting) had the single-player / offline SLOW MOTION bullet cam activate and then the players subsequently de-synced (for obvious reasons). Other than that isolated incident, the MP bullet cam has not worked for myself or my co-op cohort. This, despite having the MP bullet cam checked and the frequency set to "increased". I pretty sure it worked consistently in the NZA games...
Now, aesthetic satisfaction aside, without binoculars (which are no longer present... for some curious reason) and now without bullet cam, there's no real way to judge distance for scoped shots without essentially wasting ammo to see where the shots are going (and even this is a very sketchy measure of range). You can kill a target, of course, and check the resultant on-screen kill summary. But that only gives an approximation for the immediate area and is a fundamentally haphazard way of doing this.
The close-up of a kill (even without slow motion) and camera angle change helps a lot with assaying where bullets are going relative to one's perch. Can this bullet cam issue be fixed?
As an aside, could a toggle-able option for REAL TIME bullet cam (in single-player) be added, as distinct from slow motion cam -only bullet cam? The slow motion looks great (I'd even love to see it for explosions and other weapon kills), but seeing it ad nauseum grates and not having ANY cinematic kill cam is kinda boring. Enabling an option for the real time bullet cam / tracking would be a nice change-up and would keep the stylised mechanic fresh.