Out of sheer boredom, and curiosity as to just where the KDF might draw additional races in the future, I did a few hours of research to find some potential candidates. I'm sure this has been done before, however maybe not to this scale. Some of these selections may be fanciful, or far fetches, but hey, when you have aspergers the sky is the limit, right?
I've included some of my logic for suggesting these races, and It'd be interesting to see some peoples thoughts on individual races as they might fit in within the KDF, and possible traits for those that seem likely to you.
I think we all already know some are extremely unlikely, so just gloss over the ones that area laughable whimsy, if you'd be so kind.
Antedeans: A race known for unsophisticated thought patterns, and a distaste for space travel, as well as known for their assassins. Considered a handsome race by the Klingons. (Or at least Worf.) If their need to hibernate through space travel could be circumvented, these gorgeous fish men would be a welcome addition to the empire.
Anticans: A race of carnivorous, furry predators who like live prey, including that of sentient species, like their rivals, the Selay. They'd applied for federation status at one point, but it would be interesting if mutual conquest of them and their Selay rivals brought both into the KDF as rival races within the empire. Eager to make themselves more useful than their rivals.
Chalnoth: An anarchal society of hideous, lion like humanoids who are so vehemently against government they have none. Only the strong survive. Beaten into submission, they'd make a nice addition to the empire.
Flaxians: A visually distinctive race, known as incredible assassins creating incredibly complex kits if 'perfumes' which can create varieties of poison when mixed in various quantities. Also known to be excellent with explosives. As soldiers of fortune, they'd probably be attracted to wealthy clients. Such as... Klingons.
Kzinti: Larry Nivens superb warrior cat race from the Known Space series, also made its way in Star Trke lore in the animated series. A giant, angry race of cat people, possibly related to the Caitians. In the same sort of way that my Tabby Cat is related to a smilodon. Technologically inferior to other races, they might easily be folded into the empire if given the chance for renewed conquest.
Selay: Scary carniverous snake men , rivals of the Antica, who have the gall to eat Selay as a food source. Bitter rivals who, if both inducted int the KDF, would make an interesting pairing, what with an intense rivalry that exists between them. Theoretically applied for federation membership, but did you ever see snake men in starfleet?
Skorr: A race of warrior bird people who once had vast armires powered by advanced technology, however a recent philosopher turned them away from their warlike path towards a more peaceful path, however there have been signs of throwbacks. If conquered by the KDF, they might make an interesting addition to the empire.
S'ona: While many of them have regained their youth, I imagine many of them still feel the lust for empire that they and/or their parents felt when they left the B'aku. After their losses during the events of Insurrection and the Dominion War, they might take their technical expertise and cunning, possibly even their slaves, with them somewhere where they can accomplish more.
Tarlac: like the Ellora, with the S'ona destabilized as power in the alpha quadrant, their former slaves might be looking for some new coat tails to ride. Or, if the S'ona themselves aligned with the KDF, they might come along for the ride.
The Tellarites are a Federation founding race, not likely to go over to the Klingons after a couple of centuries in the Federation. The Kazons are in the Delta quadrant ... a bit far from the Empire to start with.
Humans, like the Tellarites, are a Federation founder.
Not really good choices for the Empire.
If some sort of arrangement could be made to use the Kzinti, I think they'd be a natural for the Klingon faction. Sadly they aren't in the main Star Trek IP and are owned by Larry Niven ... so we'd be looking at licensing fees and the like.
The Son'a are also quite unlikely given the fact they worked with the Dominion.
Assuming some kind of "True Way" faction comes along in the future they'd be
far suited to be allied with them.
Chalnoth sound nice, they respect strength and the KDF is certainly strong.
Selay and Anticans...I assume it'd have to be one or the other since they don't
get along very well at the dinner table unless one of them is dinner.
Vito'D (SP?) they scream were friend of the empire die die die everytime u meet them.
Humans = humans i can see working with/for every faction (except the undine)
Tellerite (they captured archer for the empire)
Kazon (federation got pakleds.. klingons turn to get some useless species)
Vito'D (also think they're written like this): Killed alot of them in the name of the Empire, they die easily and only work for themselves. They are no allies for the Empire.
They are target practice.
Humans: Only useful as engine fuel.
Tellarite: One mercenary doesn't make the entire species an ally, they helped found the Federation and many of them were killed by our fine warriors in the brief struggle after we withdrew from the Khitomer Accords when the Federation refused to help us in our war with the Cardassians.
One of our great warriors beheaded one of them with one stroke, he had no time to even scream.(DS9:"Apocalypse Rising")
Kazon: A bad parody of the mighty Klingons (surely Jeri Taylor's influence), they're remotely similar to us, just dumber without honor and discipline, low-tech and with terrible hairstyles.
Even the Borg refused to assimilate any of them so why would we want those?:p
I think the Skorr would be a very interesting addition.
First they don't look like all the species,
and second you could have a faction of them wanting to rekindle the glory of the past and joining the empire to seek it.