A Joni-as-mother fantasy? That's what Richard found:

In the new film, Tarnation, there is a Joni mention.

The main character's character (who is also the director, it's an auto-biography/documentary -- not sure of the genre -- very edgy and wonderful -- read about it on the website!), said he had always wanted to do a musical of his life... names some people who would play whom, and Joni Mitchell would play Renee, who is his mother and forms a central focus of the film. I'm not giving away anything here!

Miniscule Rolling Stone Review...

(Contributed by Richard)