I'll chime in with some Wisconsin perspective, as well. Most folks I
know around here who are writing art curriculums, like you, want to design
their own, to have both ownership and autonomy. I think nearly everyone
looks at their state and national standards (but primarily state) and writes
from there-meaning, you write the curriculum and then relate it to every
standard it matches-this is not as duanting (IMHO) as one might
think-although, somewhat time consuming.
That said, in our neck of the woods, we wrote much of it as has been
described, concepts, skills, etc., but wrote suggested activites very
opened-ended. So that a unit might be based around a concept, rather than a
media. That way, the teacher is free to teach the concepts and skills with
the media of their choice.