I would like Ser Zephirin to have a more prominent role in the King Thordan encounter when/if an extreme mode is to be released for him. My reason for this is because to me, he is an extremely interesting character that really didn't get a fair ending.
I personally find him interesting because of his dynamic with Haurchefant and both of them being archetype knights but in completely opposite spectrums.
Haurchefant represented justice and righting wrongs without reward. This is shown twice when he stands against the Inquisitor in Coerthas to rescue his friend, as well as when he opposes the Archbishop during the Temple Knight schism.
In stark contrast to him, Ser Zephirin represented duty and loyalty but of a far darker variety. Zephirin was loyal to the Archbishop to a fault. He obeyed and protected the Archbishop even at times when he disagreed with his lord (When he and the Temple Knights are sent away by Thordan). This loyalty of course had him directly clash with Haurchefant's sense of justice, ultimately leading to Haurchefante's death.
That is the main reason that brings up this request. Despite his fairly major role in the story, as well as being the one who ACTUALLY kills Haurchefant (Sure, Thordan indirectly is responsible, but Zephirin strikes Haurchefant down) Zephirin really doesn't have much of a role as far as player interaction goes.
We fight Ser Adephel Brightblade twice, and I literally have no clue who he is. In addition, he's represented very powerfully, being able to cause a raid wiping skill if not properly handled. Ser Grinnaux, and Ser Charibert also have prominent roles during the encounter but that's understandable.
During the 4 times I've fought Thordan, I didn't see Zephirin anywhere beyond possible Thordan's Limit Break, and at the start where he orders the Heavensward to transform into their primal forms. In another twist of irony, when the Heavensward transforms, Zephirin is way in the back, making it hard to even notice him.
Throughout the entire story leading up to the Vault, I was always curious about what Zephirin would do more than any other character. He was the loyal knight to a very suspicious Archbishop. Ser Zephirin's true character is revealed during the Vault of course but even so, I don't feel like he has a satisfying conclusion.
Maybe he could be the explanation for why there's a extreme version of Thordan at all? You go to Haurchefant's grave and contemplate the past, but then Ser Zephirin's spirit haunts you suddenly, hungering for vengeance for his falling King. He forces you into a nightmareish realm that just so happens to look exactly like the Singularity Reactor and you fight extreme Thordan with all the new stuff that would come with an Ex fight.
However, at the end when Thordan falls; Zephirin becomes enraged and tries to empower his nightmare to trap you for eternity. Haurchefant then intervenes and sunders Zephirin's power in his own nightmare realm, beginning the last phase of Ex where players would have to fight alongside Haurchefant and slay Zephirin.
Even if it's not as involved as that, I would like to see Zephirin get a larger role in an ex version of singularity reactor, if we get that.