With this in mind, I have decided to look at what other species would be an interesting addition to the game in general, and which species would be the most likely to become playable, based on popularity or prominence in Star Wars lore itself or whether any similar species have already become so.
Considering that we've seen other species from the Prequel Trilogy such as Kel Dor, Nautolan, Togruta and even Ongree realised in this game, the omission of this particular species doesn't make that much sense to me. They already have a human-like face, and if they could model the Twi'lek Lekku and Togruta headcrests, the horns of this species wouldn't prove too hard to replicate. Maybe they just aren't a popular species.
If anyone knows anything about Zeltron then immediately a problem rears its head; Zeltron are, without going into much detail, probably the most promiscuous species ever to be found in Star Wars, and considering some of the items which can be found slipping past the radar in this game, that's saying a lot. Zeltron are essentially red/pink humans, similar to how a Mirialan is a green/yellow human and Chiss a
A new addition to the game with Fleet Admiral Bey'wan Aygo in 2.6 and the Kuat Drive Yards Flashpoint, Bothans have since become slightly more plentiful. Bothan mobs can be located on the slaver island on Rishi, and the Consular can interact with a Bothan Jedi Master named Kutri O'a (pictured) in their Rishi class quest. The sole reason why this species could become playable is also the main reason why it wouldn't be very popular; people might deem them too similar to the Cathar species and just not see any reason to create a Bothan.
Popular because of the first identified member in the Star Wars lore, Kit Fisto, Nautolans in-game are unique when compared to the vast majority of other non-playable species; most individuals of these species are often the same colour as another member of their species and only ever seen as one gender or body type. Nautolans have by far the most variety in this regard, as you can find both genders in multiple colours - yellowish-green, green, and blue - and even a body-type-3 male Nautolan - although all of these specific individuals are admittedly all the same shade of dark green. This shows that there at least is some precedent for hoping that these species will become playable, as we already see much more variety in them than we ever saw for Cathar. With Togruta now beginning to push the limits on animating Lekku - three head-tails as opposed to two - Nautolan would certainly be an interesting further test.
The poor man's Togruta? Much like Bothan, people might cite the small similarities between these two species as reasons not to create one. In spite of this, and even though every single Chagrian shares the exact same stern face with the rather pointed cheekbones, I have a feeling that this species would still be quite popular. They could be another species which gains the prominent black Sith Tattoos which Zabrak and Twi'lek receive, based on the sinister Darth Wyyrlok III, famous under Darth Krayt in the Expanded Universe's Star Wars: Legacy. Much like Iktotchi, this species wouldn't be so hard to replicate after Togruta and Twi'lek.
Rhetorically slimy and naturally backhanding, Devaronians would doubtless be a popular choice for the Smuggler. Whilst many would claim that this species doesn't have a lot about them to customise, remember that Twi'leks suffer from this to a worse extent, as whilst you can change patterning on Lekku, you can't change their size or 'style' - I have seen many requests be put forward for the ability to wrap Lekku around one's neck a la Bib Fortuna. Devaronians are so far the only species seen to have parts of their body itself vary, as there are different horn sizes; a short squat pair and the more standard long and impressive pair. This in of itself would make the species quite a bit more varied than most other alien playable species are.
Much like Nautolans and Togruta, Kel Dor have a famous namesake which makes them a popular choice for many; Plo Koon. Indeed, every single member of the species in-game is a near-exact clone of "Master Plo" himself. A popular choice for sure, but if this species were to become playable it would require so much more work than any other species listed. It is the only one to not have a face with visible eyes or a moving mouth, and there really doesn't seem to be all that much to customise about the species. I feel that if the species had more varied breath masks and skin colours as can be found in various comics in the SW Expanded Universe and even in the computer game Jedi Knight: Jedi Academy, I would be slightly more confident of this species' introduction among the playable roster. As it is, this is very much the most "if only" of all species on this list.
Whilst no member of this species ever speaks Basic in the game, there are cases in Star Wars lore were Rodians do speak Basic, so therefore I am only just scraping this one by. The distinctive accent would, however, be lost in this way when applied to a player. Whilst I waxed lyrical about the in-game uniqueness of Nautolans, the Rodians would be a close second. They too are seen in multiple colours, green and purple, and you can find members of both genders in your travels. Considering the legendary scene in Episode IV, I can imagine this species being a popular choice for Bounty Hunters and Smugglers, although Rodian Jedi are also seen, including ever-so-briefly in the Deceived trailer for this game. Whilst they don't have faces similar to any other species in-game, there should be a good amount of customisation one can achieve with their ugly mugs.
A lot of new species are being integrated ever-so-slowly in this game. Keep an eye out on Nar Shaddaa come June 9th, as you may find Aqualish, Snivvian, Ishi Tib, and a female Nik'to in the casinos, all of which were brand-new with that event last year; Ishi Tib can even be found as a passive NPC on Rishi. Thus, I consider the want for more species in general to be far less significant than the hopes to see any new playable species.
Considering how long it's taken for Togruta to even be teased visually, I sincerely doubt that we'll see any new species added as being playable, but it's always nice to dream of what might be.