I'm fine with the sword users we have.
Marth-Was the original FE lord, iconic, etc.
Lucina-Probably takes approx. 2 days, max, to change the model and some move data around.
Pit/Dark Pit-See above. Also, they technically use bows that just so happen to also turn into dual blades.
Roy-Roy's Our Boy.
Chrom-Roy's Our Boy but without fire effects and some extra borrowed moves. Doesn't seem to take too much more time to make than Lucina/Dark Pit.
Ike-Greatsword user. Unique.
Robin-A mage that happens to have a sword. Unique.
Corrin-A manakete that happens to have a sick-looking chainsaw sword. Unique.
Link, Young Link, and Toon Link-Adult Normal Link should always be kept, no exceptions, and while his semi-clones leave something to be desired appearance-wise, I'm perfectly fine with having them all back for an "everyone his here"-style game.
Meta Knight-He's unique AND comes with a neat battleship.
Cloud-He exists. Also, his stage is cool. Unique, too.
Ganondorf-I forgot he uses a sword in Ultimate. Well, he's iconic, so he might as well be kept.
Greninja, Mega Man, Kirby-Do they even count as sword users?
Mii Fighter-Well, yeah, I guess they're fine. Customizable, too.
Shulk-The Monado Boi is much, much different to the other sword fighters. Unique.
Any I missed?