BlackbirdSR-71C wrote...
Yahg.
Raloi.
Prothean.
The Yahg are specifically being left alone by the Reapers for being underdeveloped (they are not savage, their technology is just on par with what we have right now in 2012). They have not yet reached their apex, and as such are spared from the harvest. To have them fighting the Reapers makes no sense because the Council would have to reach out to them for aid, rather than recruit them to fight a common enemy. And the last time the Yahg were contacted by the Council several diplomats went missing and the planet was quarantined. They are also larger than any race playable currently, including the Krogan. This would give them a titanic hitbox and would make low cover pretty pointless. The Elcor are exactly as likely to be added, because they are at least being threatened by the Reapers. Being bipedal does not mean you seamlessly integrate.
The Raloi are a one-note bird flu joke. There are no depictions of the race to my knowledge beyond "they are an avian race", which really you may as well be inventing a new race from scratch at that point. All we know about them is they are bird people, there was a disease involved and they destroyed all their satellites to hide on their homeworld and hope the Reapers pass them by. Even assuming that the Reapers did not overlook them and slated them to harvest with the other species, we do not know anything about their physiology. They could be like the Hanar, having a completely different skeleton and methods of movement for all we know. I highly doubt we would see them added to MP when they have never made an actual appearance, only one article and one casual mention ingame. Of the three, they are the least likely to be added.
Protheans are the last race that could be added to multiplayer that we are aware of and have depictions of that would seamlessly integrate mechanically. But they carry their own can of worms along with them, in that if you have enough of them to send into combat as part of the N7 forces then it severely hinders Javik's purpose in the single player. He does leave openings when he speaks about the Prothean plans to ride out the harvest, so it is not lore-impossible for there to be more Protheans fit for combat against the Reapers. However, it causes a last-of-his-kind character to become cheap and flimsy. And you cannot really make the argument that Shepard and by extension Javik would not be made aware of more Protheans being found. If they were added to the team, Hackett would be aware of it. Do you think for a second Hackett would keep information like that from COMMANDER SHEPARD? Hackett is one of the few people who truly understands Shepard's significance in the war, and would not keep him out of the loop on something that historic. They could happen, but if they do they will likely be the final hoorah for the MP DLC. A "here's your Protheans, now we're square" sort of deal.
tl;dr
Not gonna happen.
Not gonna happen even more.
Maybe, but there would be far too much whining for it to be worth it.