I use a Balmar MC614 external regulator on a Balmar series 6 alternator. It works well. It could work better if it were integrated with other Victron equipment and could be adjusted and monitored using the Victron Connect App.
Victron has all of the smarts to make an External Regulator. The provision of the alternator field current to satisfy various battery chemistries could be programmable and being able to see and modify that using the App would be perfect. Various nice features like ramping belt load and alternator and battery temperature sensing could be incorporated. It could be included in DVCC and could be available to VRM. The addition of the Battery Smart Sense would make compensating for voltage drop easy.
For Victron to include an External Regulator would make for a much more efficient Lithium solution than using an Orion.
It is the last piece of the puzzle for marine applications with significant house battery capacity.