Short stories are selling again, and writers are paying attention
Even before Amazon launched Kindle Unlimited, clever authors were using short stories. Not so much as a profit center, but as a trial balloons.
Consider Fifty Shades of Grey. Its genesis was as episodic (serial) fan fiction. I'm not suggesting that E.L. James cold-bloodedly sent up a trial balloon by creating Twilight-esque fan fiction with the idea of turning her stories into bestselling novels.
I am suggesting that what happened with Fifty Shades is worth looking at. Fifty Shades developed a big fan base for E.L. James, even though early versions of the books were available free on the Web. Fifty Shades sold massively both in ebooks and in print, and continues to sell.