I suggest "talent" to be an acceptable wish. If a character makes such a wish, and any are available to him/her, a normal "choose a talent" window would appear. If none are available, he/she would either waste the wish or get the "that was a foolish wish, try again" dialog. I understand that multiple talents for one wish would be too much, so using the plural would still only gain one talent.

Why this would improve the game
- would be a catch-up system for those characters that get only 1 talent in birth
- would give more options for wishing
- would enable high-level characters to finish a talent chain they would be otherwise be 1 (or 2) talent(s) short of

Why this would NOT ruin the game
With wish engines now being history, this shouldn't be a problem. The price for gaining a talent this way is that you could've wished for something else: SoCR, AoLS, RDSM, a certain skill etc.