I wouldn't doubt if sigurd were in...
A lot of people make mention of how much Sakurai wanted him...
True, but he was cut in Melee to make room for Roy. Sakurai didn't Marth because Marth is obviously more important in representing the series. Sigurd was going to be the Marth clone, but Sakurai wanted Roy for advertising purposes so Sigurd got cut.
Both should get in. Two spearers doesn't destroy the spear diversity, it rather gives more options. How about Blazing Sword, the one the other guy mentioned?
Blazing Sword is the first GBA FE in America (the one with Eliwood, Hector, and Lyn). Over here it's just called Fire Emblem, but since it's the 7th game in Japan it has a subtitle just like all the others. The Black Knight uses a Sword. He is able to use lances, but he doesn't in either game he's in. If he gets in he'll probably use the Aldonite.
Sword of Seals (Roy's game) is technically the first FE on the GBA, but it's not available in America.
It's not that I don't want all these cool FE characters getting in, it's just that I don't want to cut an already established, popular, important character like Marth to make room for them. I can see FE having 3 reps at most and I just think there are other characters more deserving of the spot.
The Black Knight is one of the only Major villans to appear in multiple games (the first was Medeus I believe, which is the Dark Dragon Marth fought) and is also a very popular character.
Marth is an already established Melee character and is the first FE lord. He's also 1 of the 2 lords in FE history to appear in a sequel. He commanded your army for 2 full games which still hasn't ever been done (Ike was more like 1.5). I don't see him getting cut.
Ike-confirmed
Micaiah is the newest FE lord and could easily be used to advertise FE10 Goddess of the Dawn (if Ike isn't enough). She's also a girl and a magic user, which would make her a unique character for Brawl (as long as she's not like Zelda.) It could also represent a different side of FE, showing that it's not all about swords (Ephraim could do that too, but a magic user would be more of a contrast).
He's got quite a bit of competition there.