I think some of the fanfiction prompts would work but others seem a little too specific or hard to translate into a drawing. Here's the fanfiction prompt schedule:
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January 2018 (January 1 – February 15)
Incorporate the following into your story: ”He (or she) had once imagined becoming the leader of the herd. But not like this… not like this.”
February 2018 (February 1 – March 15)
Write a story about "undying love." What exactly this means is up to you.
March 2018 (March 1 – April 15)
Write a myth or legend set in the Land Before Time universe
April 2018 (April 1 – May 15)
Nothing to see here, folks. Move on!
May 2018 (May 1 – June 15)
Incorporate the following phrase into your story: “when the bright circle rose the next day, it rose over a very different Great Valley.”
June 2018 (June 1 – July 15)
Everyone writes a prompt of their own choosing, then the prompts are shuffled and redistributed back to the writers. The writers must then do a story based on their new prompt!
July 2018 (July 1 – August 15)
Your theme for this month: there comes a time in everyone's life where a choice must be made, one which may irreversibly alter the path ahead.
August 2018 (August 1 – September 15)
Goodbyes are never easy. Write a story about a parting.
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Prompts like January, May, and July seem like they would be really hard to do. February seems reasonable and March and August could maybe be done but will probably be harder. The June idea could still work as well. Overall I would think keeping the prompt ideas for drawing to be a bit more on the simpler side of things
I do like the idea of drawing fanart from a fanfiction response (though it would be best if we drew the previous fanfiction prompt responses then we wouldn't have to wait). It might be cool to always have this option as a substitute if there is ever a fanfiction that you would want to do fanart of.