It's hard to do any real math on what's hot, what's the next big thing, etc in sci fi/fantasy.
Because, IMHO, what's popular among regular readers of the genres had in the past been largely determined by what's available.
In the 70's and 80' and even 90's, many of us simply devoured what was available on the the meager SciFi/Fantasy tables or shelves at our local book stores. We were stuck with what some Suit Desk Thing thought would sell. I loved James H. Schmitz's Witches of Karres and Hub series, Keith Laumer's Bolos, and most everything Andre Norton set her pen too. But Those gems were crowded out by the mindlessly nihilistic "He dies, she dies, everybody dies because humanity sucks and will always suck" drek of the 70's, then by the gibbering swarm of David Eddings Mongoquintodekaologies and a flood of TSR Dragonlance derivatives. (I liked Eddings, for a while, and even the early dragonlance stuff, btw.)
The stuff I wanted was harder and harder to find, but even the Meh stuff was still more to my tastes than reading some artistic literature of our age! drama about a girl who drank a glass of water and was sad, then coped with her feelings about glasses, water, and feelings, which were a metaphor for something or other like the paralleled plight of polypedal Portlandian Pimento Pickers.
(And I confess, I have to this day not educated myself on Portland, pimentos, or the average number of feet per picker, much less their plight. I mean, I know a pimento is that little thing in the olive, but I don't like olives or drinks that involve olives, so pimentos and I have only a nodding acquaintance. And I think they really have no idea who I am and are just being polite. Plus, I don't think I know anybody from Portland).
So I'd hold my nose and buy the latest in some mega-serialized regurgitation of somebody's D&D campaign or whatever, and treasured the odd gem when I could find it. (Godstalk, I'm looking at you. That's right. Who's an amazing fantasy and brilliant bit of storytelling! Awww, that's it! You are! Good, book, Godstalk! Yes you are! Gooooood book!)
Between the Rise of the Indie Publishers and the E-Publishers, I think that "what's hot/next big thing" is really only going to matter to writers trying to get on board with a middle to major publishing house. Getting our books out, getting readers, and maybe even being able to buy a little people food once in a while is vastly more accessible to us now, without having to try to find the right star to hitch our wagons to.
I'm by no means denouncing the idea of pursuing publication with a big company, I'd love to hit that point someday. But in all likelyhood, if I ever do manage that, it'll be on the strength of what I e-publish.
The project I'm working on now started out an attempt to fit one of the "book gigs" Kristine The Wonderful kindly shared, where a small house was looking for dystopian/post apocalyptic YA submissions. About 20,00 words in, one of my betas pointed out that my Sciency Stuff was going to be above the YA novel. And a lot of "every day" stuff would be too. ("So I got out my monocular and shot a couple azimuths...") wouldn't fly with an audience looking for sparkleopyres and such. My protagonist doesn't have a mystic heritage, a quirky genetic ability, a mentalist cat, a birthmark, or even a boyfriend, and she's quite happy that way, thank you very much.
Then I realized that I'd missed the Dystopian bus too. The story unfolded in a way that it was about preventing a dystopia rather than coping with one. I did get the post-apocalypse part right, though.
I despaired of getting it published, because the publisher I was initially shooting for wasn't going to jump on this rascal. I started hitting the "Submission guidelines" of every book house I could think of, and I despaired some more when I realized I'd be in a process of submitting, waiting 4 months to a year on average before I could submit the same work to another publisher.
Lots of despair.
Tears of it. The really good stuff. Robert Smith wishes he could manage that level of despair. His hair is too bigbigbig for him to truly know despair. Fumes from the gel.
Buckets of despair, carried by sad, despairing workers off to the despair refinery where it would be refined into distilled despair that would make the Rainbow Unicorn go on an absinthe bender and kill itself at Edgar Allen Poe's grave.
I mean, who's going to jump on a far-future , frontier setting, pre-dystopical, post-apocalyptical book which combines hard science and some steampunk elements in a rational, reasonable function? (No Absurdium Powered Etherial Rays.) It's not going to fit any sub-genre tightly enough for a publisher to say "Ah! Steampunk!" or "Ah, Hard(ish) science!" sort of way. (By "Hard", I mean closer to B5/BSG tech base than it is to any thing Star Trek/Star Wars flavored.)
I did some more despairing when I realized that a small Indie publisher might, maybe, possibly consider it, but the thought of being found only on the shelves of exactly 4 stores in western Oregon didn't fill me with yah-yah juice.
I can't write something I'm not into, it just doesn't work. It's like attempting to approach serious painting with the mindset of "I'm going to paint a '9'." (I always felt sorry for that poor, sad bastard. Poor guy, in his little hat and smock, just wanted to paint his damn "9", but they never let him. Christ. Now I'm depressed.)
Maybe in years to come, if I'm able to master the basics of the craft and the mental discipline involved, I'll be able to pick a genre or theme, sit down and crank it out. But in the meantime, I'm following the Deposed King's lead into self e-publishing, to get my invisible friends out there to play with strangers and take their candy, get feedback on my storytelling, from average readers to professional critiques, and maybe, just maybe... be able to buy some people food, like a grape, with the proceeds.
So don't ignore the trends in genre and popularity, learn from them, ride them if you can and if it suits you, but don't let them limit you.
I'm not kidding about the grape.