I was thinking there would be a passive and active set for each Aspect, but this is a workable idea too, I suppose.
As for your idea freeform, a unique skill based on your Full Title, that could be incorporated, rather than be the entire thing. But for that, in addition to giving the Aspects more concrete definitions (especially the aspects of Rage, Blood and Doom), we need to understand the classes better as well.
So, the Thief and Rogue have already been discussed in comic, as well as the Bard and Prince.
On reflection, I think the Prince stands opposite the Bard. The Prince is a Destroyer class, and the Bard, which invites destruction through his aspect, so there is the passive, active thingy.
Maids and Knights would appear to be two sides of the same coin. Knights protecting with their aspect, Maids protected by their aspect. So the Maid class, instead of as it is now, where it's a high mobility blitzkrieg type class, would be more... tanky? I guess? So Mikhael having some kind of Mindcrush power doesn't make too much sense. By my logic.
SirAaron is right of course with the Seer/Sylph class pairing. I'm not certain what abilities the Sylph class would have though. Perhaps, by default, they are healers?
So, we are left with the Heir, the Mage, the Witch, and the Page.
The Heir inherits, by the most base interpretation of the title, and John did gain a lot in terms of power and strength across the story. Then again, so did everyone else, and I have no idea what Equius inherited.
The Mage, in canon terms, is something of a mystery to me. I was thinking a few days ago it could be defined as 'One who Understands x', but I have no idea what led me there in retrospect.
Not too sure about the Witch, either. If nothing else, my gut says Active.
No clue about the Page either.