The problem with this lies in the lore and Larians commitments. Playable illithid are in Xanathars I think and they are not going to include non PHB material. The other problem is that illithid cannot really work against one another. They slowly wither and die without connection to the overmind and will do pretty much anything to be able to return to this state. Imagine if you slowly lost your ability to breath or eat if your community decided you are working against their interests. There is also the problem that the only thing that can feed them and sustain them is a combination of biological brain matter as well as the consciousness and psyche of sentient intelligence a.k.a humanoids.
There is no playable illithid race in 5E. Xannathar's book has some monstrous options such as goblins and the yuan-ti, but that is how far it goes. 3.5E had an illithid option for players as monster class levels, but that was never really a playable option for most games, maybe epic levels. I do expect however that Larian will introduce some of the non-PHB races, since they've already included some options for the tieflings and half-elves that are not from Players Handbook.
Also, you mustn't forget that mindlayers are completely alien, almost Lovecraftian horrors that seldom have any need to form any social connection with lesser beings (AKA. food or slaves). There are individuals that break the norm, but their thoughts and reason should still be too alien in my opinion.
