According to the Core Rules, a Prestige Class can never be chosen as a favored class. However, in the Advanced Races Guide (ARG), half-elves can purchase the Feat "Multitalented Mastery" which makes all of your classes into favored classes. Because the precise wording is "All of your classes" and not "All of your core classes" it would seem this feat enables half-elves to treat prestige classes as favored classes (presuming the character have this feat). And since the ARG was published after the core rules, that would give weight to this idea, since the usual presumption is the most recently published document takes precedence...
But is this presumption correct? Can a half-elf treat prestige classes as favored classes, if they have this feat? Or should the feat's text be edited to say "All of your core classes" instead?
I would personally rule that it works. I think that your interpretation is RAW correct.
The power of this feat would be similar to Favored Prestige Class, and wouldn't stack with Favored Prestige Class, which is required for the all-powerful Prestigious Spellcaster.
So, it's not like there isn't precedent for gaining favored bonuses from Prestige classes, and it shouldn't harm anything whatsoever.
My thoughts are that the RAI (Rules As Intended) is simply to expand the Multitalented racial trait to encompass all classes that would be eligible to be taken as Favoured classes, so it wouldn't stack.
The RAW (Rules As Written) could be interpreted 2 ways. The first agrees with what I assume the RAI is saying, but the second ways is that "any class" includes prestige classes. Since this feat is likely considered a more specific rule than the general rules for favoured class bonuses (and specific trumps general) this means it would work as you wish it to.
Personally I can't see how this could be over-powered, so I'd let you do it. There are no racial FCB's for prestige classes and this is costing you a feat, so 1hp or 1sp per level isn't going to break the game).
It's really good for extensive multiclassing compared to toughness or cunning.
Only if you have more than one class with a racial FCB that's better than the standard 1 hp or 1 skill rank, otherwise, Toughness or Cunning will always be better (and vastly so). And prestige classes don't ever have racial FCBs...
Seriously, I have a hard time imagining a character where Multitalented Mastery isn't total crap. Going into a prestige class makes the feat weaker, despite it working.
I pretty much exactly agree with that Derklord.
What if you've already taken Toughness and Cunning?
Only if you have more than
onetwo class(es) ...
You have to have at least 3 classes for this to be useful. Without this feat you already have the multitalented racial trait.
Each character begins play with a single favored class of his choosing—typically, this is the same class as the one he chooses at 1st level. Whenever a character gains a level in his favored class, he receives either + 1 hit point or + 1 skill rank. The choice of favored class cannot be changed once the character is created, and the choice of gaining a hit point or a skill rank each time a character gains a level (including his first level) cannot be changed once made for a particular level. Prestige classes (see Prestige Classes) can never be a favored class.