This is a relatively minor gripe, but a few folks chattered about it.
The Adeptus Astra Telepathica background grants the Sanctioning trait as their Background Bonus, removing the Corruption gain from being a Psyker and granting the character fluff status as a legal Psyker. Anyone without this is considered to be a Rogue Psyker.
This is a funny little thing because one would assume the Mystic role would include Sanctioning, as the vast majority of Mystics (for Roles are supposed to encompass the "average" archetype of such a thing) would be Sanctioned. The Psyker elite advance is right there for anyone who wishes to be a Wyrd, Witch, or other such rogue.
The lack of ability to purchase the Sanctioning trait with xp means all Psykers who do not choose the Adeptus Astra Telepathica background are rogue. This gets in the way of one of my much-beloved characters, who was a Psyker attached to the Guard. The skills, talents, and gear granted by the Imperial Guard background suit him much better than the Adeptus Astra Telepathica background, but he's certainly no rogue!
The same goes for a character belonging to one of my friends, who was a Psyker employed with the Adeptus Arbites. While he could go Adeptus Astra Telepathica - Seeker, and then purchase the Psyker trait, this seems a bit counter-intuitive.
Meanwhile, another old character of mine - a former psyker-handler who specialized in dealing with witches - would certainly have the Adeptus Astra Telepathica background, but gains nothing from the Sanctioning trait. As it is, the AAT background bonus offers nothing to non-psykers while enforcing a limit on them that restricts character concepts.
While all Sanctioned Psyker do endure the AAT, some are better defined as characters by their later work. The best solution to this is to offer Sanctioning as either a trait of the Mystic role, or allow it as an Elite Advance. To make the AAT more appealing to non-psykers, a new bonus should be considered.