Krakia?

Ah. I think many people (including myself) just assume it to be Krakia for a few reasons;

The quest with Icebyrd Slimm says we have to go to the Krakian jungle next at the end of it.
Magatia was released and told the background of Dr. Krakia.
We've been having the Thanksgiving Krakia Turkey event for a couple of years now.

If its more Masteria, Krakia really feels like the natural progression, the only way they could do otherwise would be sandwich something in between, that contains even more Krakia buildup.

But there's also the city in the calendar, and we know Krakia's a lost city off in the jungles of Masteria. Dr. Krakia, the opponent of Foxwitt who clearly associates himself with this supposed expansion, is able to time travel and created those mechanical turkeys. Because of the ability to travel into the future and the obvious ability to construct robotic nuisances, the futuristic enemies in the calendar image may very well be of this man's doing. The puzzle pieces fit, not sure why people don't understand. This image obviously signifies it's gotta be Krakia, it's not solely based on the last Masteria quest we have.

Not sure if anyone's also pointed it out, but the fact the city is placed behind the foliage supports the concept of the city being lost in the forest since you can't exactly see it unless you've gotten so close.

But for the sake of argument, let's just say for sure it's custom content and we should be excited for it.