When trying to judge the quality of your work--i.e., whether your writing is publisher-quality--would you consider appropriate practice to write "public" fanfic--that is, fanfic posted on sites such as this, wherin you will get a great deal of reader response, a feel for readers' wants and needs, etc.?
Is that the main reason people post fanfic, though?
In the 80s, ST fans often dabbled in ST fanfic, some because the act of writing it served a purpose (and they stuck the stories, unread, in a drawer), and others pursued ways to get it published in fanzines, or they published the zines themselves. In many cases, an amateur/fan editor would help shape a story just as a pro editor would help a pro author shape a story. Self-published items often did get anyone giving feedback until the zine came out. Fans with lots of disposable income tended to be the editors/publishers. There was that definite thrill of holding the fanzine in which your story was published, and to watching the piles of zines diminish on huckster tables at conventions. Hard to get that thrill uploading text to a BBS.
Any "feel for readers' wants and needs" often came only when no one bought issue #2. Generally, you get what you pay for, and a zine putting out quality material generally did well, went into reprint, built up a following. Letters-to-the-editor were pretty cool if someone mentioned your story. The difference with online fanfic publishing, I always feel, is that
anyone with a keyboard and an Internet connection can upload it. There are no editors around to say whether a fanfic story is excellent or poor, or whether the author should go back to the drawing board. A "feel for readers' wants and needs" is also extremely tricky when no one is actually paying out money for the stuff.
Do readers "want" and "need" quality ST stories, or simply free ones? (Because there are now hundreds of professionally published ST stories, and who has the time to read all of them, let alone the great unwashed piles of fanfic.) I would think potential pro authors should be more interested in pro editors' reactions to stories. Which is why John Ordover used to encourage potential ST authors to get
two regular science fiction novels published first, before pitching ST proposals and sample chapters to Pocket Books. A big ask, but ultimately doable, if you're persistent enough. And talented enough. And lucky enough.