I wonder if they'll be sticking with dueling / Zellbrigen.
Seems unlikely. Historically, the video games have not enforced it outside of trials in which the player is alone and enemies are scripted to stay out of the fight unless fired upon, otherwise waiting their turn to fight, if they're there to fight at all. The closest the games have gotten to enforcing it outside such settings has been lancemates refusing orders to specifically attack certain named enemies in
MechWarrior 4: Mercenaries, but that was not limited to the Jade Falcon characters Jeffer Roshak and Aisa Thastus, but many named Inner Sphere enemies as well; additionally, ordering them to fire at will or simply leaving them to their own devices, they would wind up attacking them regardless.
Theoretically, a full Star of human players could self-impose it as a sort of challenge run, I suppose, but I expect they would not be able to keep it up very long before it consistently and legally becomes a full melee anyway.