So, I often ask these potentially dumb-seeming questions, but I like the opinions of others before I just try something crazy in a game, so here it goes.
So, I am flipping through Dark Heresy and Ascension, and I come across the Burning Princess (Ascension, p.197). This intriguing, ridiculously-powerful Alpha-Level psyker has a Psy Rating of 14. I often look at the write ups in Ascension and say "why can't you tell me how they leveled up? If I wanted to build a different, but comparable Imperial World Governor, like Malaki Vess (Ascension, p. 199), what Rank equivalent is he, and what Career Paths built him?" In the case of BP, I don't know how they gave her a Rating higher than Eldar Farseers by quite a margin, and don't know how it would be done in a game, if you had a character who wanted to be really powerful, like Eisenhorn or Gideon Ravenor. You could push Psy Rating 6 with Imperial Psyker, and squeak it up to PR 10 with Primaris Psyker, but that still falls short, unless you are making judicious use of Elite Advances, which Inquisitors might do, but without having the progression option of PrPsy, and paying out the bum. I also assume that Elite Advances breaks the progression for Imp. Psykers, meaning they'll either have to wait a long time to increase again, or they'll only increase further by more Elite Advances.
So, how might one get to Psy Rating 10-12 without having to be Rank 16, and please don't just say "You wouldn't, that's part of the balancing of the game"? She might also be a servant of Tzeentch, but I don't know that, for sure. Would the Elite Advance option cost 1,500 xp each, like the option for Inquisitors/Interrogators, or maybe 1,000 xp, like the "regular" EA for Ascension? These numbers would push rank up fast, and be as rare as the 1000 xp. Could there be another mutation that enhances the mutation being a psyker even is? Do Eldar characters use a different mechanic to get up to 8, without being really high rank (I suppose a Farseer is a really high rank, but I'll ask anyway.)
How might you make the Burning Princess to get her to PR 14? Any ideas?
). Sure, we'll usually assume that the GM won't be letting me play a Farseer, and thus its rolls will be behind a screen, and Phenomena will thus only happen when appropriate, but a mechanic might still be nice, just in case the GM did take leave of their senses, or in a game where one of those rare alliances happens, and the Acolytes/Throne Agents need to have Eldar assistance to fight a Tyranid or Ork incursion, and, being the game's premise, an Eldar PC might be appropriate, once.