I think the market is looking for the next big thing. Which is vague, I know, but nobody will know what it is until it comes out. Basically, the next big thing is pushed by the next big author. The next big author sets the trend, and it sparks a certain creativity wave that is reflected with bunches of new authors. It could be anything.
The first fad that I have personally seen is dark urban fantasy; Anne Rice, Laurell K. Hamilton, Jim Butcher, Tanya Huff, P. N. Elrod, Patricia Briggs, etc. It's still going on, but I'm not sure how much longer it can go. I entered it early; I picked up LKH when I was 12 (about 10 years ago), and I didn't touch Jim Butcher until a few months ago because I was overtly jaded about urban fantasy and I thought it would suck (Ha!). So for me personally, interest is flagging. But I can't tell if it will die down for others or not; perhaps it will become an enduring sub-genre of SFF, much like how Tolkein-esque fantasy is still big (when done right).
Sub-Fads in Dark Urban Fantasy:
- Sexy, Erotic Vampires (the biggest fad)
- Witches/Wizards (well, it's fantasy) in The Real World
- Werewolves (the second biggest fad)
The second fad I've seen is erotic fantasy. Anne Bishop, Jacqueline Carey, the crossover fantasy/romance imprint Luna, and there's this knockoff of Carey's Kushiel series I've seen, but I don't recall the title or author. Also, I think this is churning around with all the slash fanfiction online, some of which is very hard NC-17, feeding on itself. It'll probably explode into mainstream in a much bigger way soon, we've just seen the first shots.
As for "backlash vamps"; I can't say if it will sell. It might. E. E. Knight has alien vampires, and he sells. Then again, alien/parasite vamps is just a sci-fi spin on the fantasy mythos. There's a line somewhere that says, "if the amazing thing/creature/whatever is done by magic, it's fantasy, and if the same thing is done by a machine, it's sci-fi." That's what people are trying to do with vampires, and I don't think it will go over very big, myself, or maybe I'm just biased and I don't like it. Mostly because it's so obvious, it's a staple of the SFF genre to flip something like that. Tired of big sword-weilding barbarian men? Have big sword-weilding barbarian women instead! Tired of evil fantasy dragons? Let's have good telepathic alien dragons instead. ::coughPerncough:: Tired of Dracula-type vamps? Let's make 'em alien and biology-based instead of Evil and dead.
Things that I think might make it big are:
- demons (hey, vamps and werewolves have been done.). Then again I'm biased here, as my biggest world has many demons.
- Epic Urban Fantasy (I think Jim is pushing the Harry Dresden series this way; it's basically a merger of dark urban fantasy and epic fantasy)
- non-gritty Urban fantasy/fairytale urban fantasy (things have been Gritty so long I think Heros and Flowers and Sunshine are going to make a comeback despite false cries of Mary Sue)
- fantasy based on some mythos we aren't familiar with (yet)
- christian fantasy (fantasy in general has really been kicking christianity around for years and promoting wicca and new age religions. I think this will backlash; I'm not even christian, and yet I really like Jim Butcher's Carpenter family, because it's christianity treated with respect, which is so rare in the genre.)
Eastern and Asian fantasy have potential to be hits, look at the popularity of Manga and Anime, except for the fact that SFF is mostly a Western European genre, and most authors are white middle class western folk, and don't have the roots in Asian culture to really do it right. (Sort of like Historical fantasy; to do this you really have to do your research.)
African fantasy is entirely untapped, even more so than Asian fantasy. This could go over really big, but then again, there aren't many black writers in the genre so there aren't many people who have the urge to really dig down to the roots and do the research to make it work.
Anyway, those are just some of my thoughts and opinions.