Werewolves have already waned a bit, but I've heard about people having success with more generic "beastmen". I honestly don't know what that means, but it makes me picture 80s Beast. Everything else tends to flop, which makes me sad - goofy fantasy stuff is my favorite to write.
If you want a good way to check whether kindleporn is successful or not, check out the Amazon sales rank. There's a bit of variation but ~300k is a few sales a month, ~800k is a sale every other month or so, ~150k and up is where it starts to be successful... anything under 100k is selling well. It seems to depend on how many total sales the ebook's had, how old it is, and how recently it's had sales. New releases tend to have lower ranks, the lower the better. For reference I had a story that hovered between 150k and 90k rank when it was bringing in about $100-$150 a month.
What I'm saying here is don't look up Peter de Sade from the F+ kindleporn episode, you'll get depressed at how well his horse-dick stories are doing.