Lemme rephrase that: of Veteran fighters between the three series (hence why I said the vet retro fighters).
FE seems like it should go first, considering its likely going to have at least three characters. Although Sakurai could end up being bone-headed enough to throw in just Marth and a Chrom that is basically an Ike-reskin.
Its really odd how Sakurai has confirmed every Mario veteran, yet series like FE have not even had character confirmations yet. And other series like Pokemon, Kirby, Star Fox, and Zelda were all basically stand alone (Zelda would have likely remained stand alone had it not been for Wind Waker HD).
I think it will basically be a free-for-all in terms of veteran confirmations once we get past Q4 2013.
The only remaining software releases left that could be tied into a possible veteran confirmation are Pokemon X/Y, Zelda: A Link Between Worlds, Yoshi's Island 3DS, Kirby 3DS, Donkey Kong: Tropical Freeze, and Mario Kart 8.
The overwhelming majority of veterans won't have a new software release that can be tied to their confirmation.