My only issue with psionic classes is that in my 5e campaigns, the "spells" and abilities of aberrations, like Mind Flayers are treated as not magic and, therefore, not subject to being dispelled, antimagic fields, magic resistance, etc. Keeping that ruling could still work, but I think it would work best in a campaign where you enemies with psychic abilities play an important role. More likely, I'll just run it RAW, with psychic spells and abilities just being a flavor of magic.
This is also why adding psionic classes feels pretty "meh" to me and why I don't have much of an issue with having them in my campaign. Whether academic research, divinely granted, less-godly supernatural entity granted, ki, or psionic power, its all just a flavor of magic. It really doesn't change anything.