Dem Top 10 Elitists!
Crazy to think that just a few years ago the top 10 was dominated by FPS... now it's Open World. What comes next?
I feel the trends have often followed the strength of what the newest consoles allowed, but that's becoming blurrier now.
Like online gaming got a huge boost with the 360/PS3, so we saw a ton of shooters (both competitive and co-op) taking off.
Near the end of last gen developers began pushing open worlds more and more as they were preparing for a very RAM heavy future that could open up their games a lot, and some of their heavy streaming technology allowed these games to show up on last-gen as well. Similarly we saw a lot more online connectivity taking off as they had lots of spare RAM and a better connection pipeline than existed before.
At this point, what's there that is really gated more by the physical hardware than the budget of the games? I don't think there's an obvious answer.
One area I do feel that's still underutilized though is co-op RPG progression games. We've seen Borderlands be a huge hit, Diablo 3 be an insanely huge hit, and Destiny be one of the biggest if not the biggest new franchise this generation. However, we still don't have a lot of games that are sitting there and trying to compete with that directly. It's basically the idea of scaling down an MMO into something where you can have more action oriented combat and have the players feel like they're doing a lot while still having all those other hooks in play.
There also seems to be a slow rolling movement into how to make MOBAs work on consoles since a lot of publishers seem to view that as an untapped market that could conceivably compete with shooters. Take-Two's 2K unit said that they're putting their biggest launch ever behind Battleborn (I'm assuming this is delayed to 2016 at this point?), Microsoft and Sony are courting and/or developing MOBAs internally, Activision has a lot of MOBA influence (combined with TF2) in Overwatch, and even games like Black Ops 3 are taking pointers from how MOBAs design their heroes with the multiplayer characters (and notably they're characters to boot) in its multiplayer modes. The popular answer here seems to be "try and merge them with shooters".
Beyond that, I'm not seeing a too much of a third emerging trend on the retail AAA side of things beyond more investment in what already works. I guess people are perpetually trying to get music games and racing games to work again, but I'm not sure how much gas is left in those tanks.