I recently figured out a potential way to make a balanced psionic class, but I haven't made the time to examine the mechanics that I have in mind yet. I'll be posting a Mystic/Psion class on my DMsGuild channel, probably in the Spring, Summer at the latest this year. I might also use what I have in mind to revise the existing Shaman class on my channel with the new mechanical structure that I've been thinking of. It will definitely be different in a noticeable way from how the Unearthed Arcana attempted to balance the Mystic. I could share my blog links if you want to keep track of my design work, but a psionic class design won't be coming for at least a couple of months.