Michelle Ruff provides two of the three voices for the female Avatar, both of which sound more than a little reminiscent of Yukari Takeba.
I Knew It: When Male Morgan was confirmed as the boss of the first Future Past DLC Chapter, some fans theorized that Female Morgan would be the boss of the second chapter. They were right. Even less people were surprised that the third and final Future Past DLC Chapter's boss turned out to be Grima.
Jossed: It has been theorised that Lon'qu, the swordsman who Cannot Talk to Women, would extend his awkwardness around them to his own prospect daughters from the future, should he marry a first generation character who gives birth to a girl. The Future Past DLC josses this: if he marries Tharja and then he goes rescue the alternate universe!Noire, AU!Noire bluntly mentions his aversion to women, and Lon'qu's reply is basically "why would I be scared of my own daughter?". Granted, conversations with other potential daughters suggest that while he is unafraid of being near his daughter, he was afraid that he might.
Marth Debuted in Smash Bros.: Thanks to the SpotPass optional battles and paid DLC, HEAPS of of characters from FE2, 3/12, 4, 5, and 6 are appearing in English for the first time ever in this game. Marth himself averts this, having previously appeared in Shadow Dragon.
One of Us: If his Twitter is anything to go by, Kaiji Tang, the English voice actor for Owain, is an avid player of the game himself.
Subverted with Lucina and Lon'qu, though. Even though their voice actors (Laura Bailey and Travis Willingham, respectively) are married in real life, they can't be paired up themselves because the only character who can marry across generations is the Avatar.
Serendipity Writes the Plot: Why Morgan has amnesia, as, depending on whether the Avatar marries a first or second generation unit, Morgan would have wildly different backgrounds and would require numerous script changes to their Supports. Amnesia easily circumvents this problem.
Talking to Himself: Insofar as Voice Grunting allows, given doubling up among both casts. Especially notable though with the mother-daughter pairs Sumia and Cynthia and Cordelia and Severa in the respective dubs (Ayano Yamamoto and Julie Ann Taylor respectively). Also Donnel and Stahl share the same English actor.
Some of the fathers and sons can end up talking to themselves if you pair the mothers up appropriately: Lon'qu and Brady, Kellam and Gerome, Gregor and Laurent, or Yarne and Robin (if the right voice option is picked on Robin).
What Could Have Been: Early trailers indicate Sumia was planned to have Cavalier as a reclass option.
In earlier trailers, Garrick (the Barbarian boss of the prologue) was named Grendel, but this was changed for unknown reasons.