Perhaps I should start a new thread: What kickstarter based deck would you consider to be trend setting? Take out all the xxxpunk decks, zombie decks, lovecraft decks and cheesy cheese. And yes, Federal 52 is a good example of trend setting.
Don't get me wrong, I'm not seeking ideas as I am on my final deck and then I'm back to designing board games. I'm just a huge fan of statistics (from my advanced studies in demographics and population)
There's a few possible trends.
As Emmanuel stated, yes, circus/carnival is trending. I think that "Carneval" would be a much more interesting trend, though!
I look at the Rebels deck and the various iterations of Federal 52, as well as the Founders - and wasn't there a Lincoln deck BEFORE the Pixel Lincoln deck, a slightly more serious-looking deck? Or did that one fail? So there, I'd say that Federal themes are trending up.
After Synthesis, I wouldn't be surprised to see cyberpunk trend up. There seems to have been a mini-revival of the genre since the new Tron movie. Also in this trend is The Grid and Grid 2.0 - arguably The Grid was the kickoff of this trend.
Zombies, Cthulhu, Steam/Gear/Clockpunk - still trending but I'd say due for a plateau soon enough. A straight-up Victoriana design, however - new possible trend. Examples would be Timeless and Vict, and maybe Bicycle Amazing Adventures, though one could argue it's more 19th-century-pick-your-own-punk. The Americana deck would be the "proto-deck" of the trend, less for the faces, more for the back design - something that's genuinely true to the era - though a multi-color back like that in the age of the Old West would have cost a pretty penny indeed.
I'm seeing a number of new decks extending the "Vicky" historical trend into the early 20th century. A few decks have been using Art Deco typefaces, there's a "Deco" deck coming from Encarded/Paul in the near future, and the "Butterfly" deck looks like something in-between the age of Art Deco and Victoria.
And speaking of "Pixel Lincoln" - I see "8-Bit" as becoming a huge theme, especially with the successes of Home Run Games recent decks in that genre. Imitation is the most sincere form of flattery, and I predict some artists are going to flatter the hell out of them!
Beyond that, try pouring over the New Deck Report like I do when I have to write it - if you're going to find a trend anywhere, that's the place to start looking. The 2013 Releases topic is also good research material in that area of study.