Seeing as this IS the Writers Desk. I feel personally it should focus mainly on writting challenges. Though I would like to see some of the collabs as well with Artist Easel. I just wouldn't focus on that too much. The challenges themselves having no limit sounds good for freedom to go wild with whatever you can imagine. Though with limitations you could use thoughts of a "part 2" if you ever wanted to a challenge.

I do like the idea of a mystery exchange, but like Gemma said. You'd need a lot of volunteers for that to go over well. You may not want the same people, all the time for it either. Someone different to change it up at times.