Knowledge skills should have encompassed this, and should have been ranked like languages. Can’t remember the edition maybe 3rd but they had background skills to cover things that aren’t skills that really help on a run but are still valuable to flesh out your character.
I agree that they should have been ranked the same as language skills. To give it more flavor, the third tier would need a specialization, and the equivalent of native level (Savant, maybe?) would require a further expertise.
But I don't think they should be lumped in with knowledge skills. A character knowing a lot about art may be able to tell you everything about a famous painting, but that does not mean they can paint to that same level.
Same as in same karma costs. You might have KS Dani’s artists and also the background skill painter. They both do about the same for your character in play so have them both cost the same karma.
