The urge to write really bad fanfic does, in fact, come upon me at times, so I'll definitely keep the possibility of some Eight/Roberts!Master open.

I was actually going to say another thing but didn't, and that is that original fiction writing, lacking the pre-made world and potential for fan interaction (whether direct or indirect) is is so completely in a different ballpark that I don't think it's a logical expectation that writing fanfic leads to or can be interchanged with writing original fiction. The function of fanfic as a tool of disagreement, explanation, exposition, etc. of canon characters is missing, so there's got to be something else driving the will and ability to do it. Not that I would know what that something else is. I couldn't write original fiction to save my life.