As most of you know, according to the Player's Handbook, it isn't possible to cast a spell while wearing armor you aren't proficient in.
Have there been any rulings on this in regards to expending psionic focus, or using a psionic spell? Check this excerpt from Unearthed Arcana:
Psionics and Magic
Psionics and magic are two distinct forces. In general, an effect that affects a spell has no effect on a psionic effect. There is one important exception to this rule. A psionic effect that reproduces a spell is treated as magic. A psionic effect reproduces a spell when it allows a psionic creature or character to cast a spell. In this case, psionic energy taps into magic and manipulates it to cast the spell.