@Barbasol: While Gharnef isn't the final boss by any means, he's still the one who revives Medeaus and sets most things in motion (and possibly was the one who killed Marth's dad) Though if there is any parralel in FE10, it would probably be Sephiran (or with FE7, Negal)
Still, the fact that he's not an exact counterpart to Marth is what makes him more appealing for this sort of game, since that means he's not the same thing. The Black Knight is the same thing as Ike only on the opposite side and in a lot of armor, and given his story and weapon of choice, he's pretty much obligated to be a clone. Gharnef on the other hand is in no such position.
What I was more getting at was, is there any sort of personal connection between Marth and Gharnef?
For example, in Star Wars. The Emperor was without a doubt the evil mastermind MAIN villain, but Darth Vader is the enforcer and as a personal connection so he really is the villain of the story, but not the events. Same goes for Black Knight in his two games. He's not the main villain in terms of the entire war like Ashnard or Sephiran, but he's the main villain for the story being told.
Eh, that's not really true in terms of the Black Knight being Ike in armor, I shouldn't of given you that impression, I was drawing more parallel in terms of their position in life and siding. Black Knight is also the one who put Ike's overarching development into motion. He was a student of Greil and like Ike, was driven by the need to excel and become a great warrior...
Their fighting styles are also actually quite different. Ike is more of a fight with heart rough'n'tuff mercenary. The Black Knight is a more emotionally repressed strategist. While Black Knight is likely a heavier character than Ike, he is not the same style of fighter. He has been blessed by the goddess Ashera, and as such, has access to many different spells and enchantments, such as his blessed black suit of armor. Not to mention he can also use lances.
I'd imagine that if he were made playable, he would be a heavy character with strong attacks, but also has magic attacks and movement abilities. There's several directions that could be taken with the character. So, I REALLY would cringe at the assumption he'd be a clone.
EDIT: One cool gameplay option that should be given to an FE character should be a Bv Weapon Swap, it's important in the games, so it would be cool to give to a character. Say like with BK (Obviously I am referring to Burger King), his sword is more powerful and slow with shorter range, but could be swapped out for the fast, long-ranged lance.
It would be very cool to incorporate as it wouldn't quite be a transformation, but it'd change a style quite significantly. It's quite important in FE because the weapon triangle.