It's proving extremely difficult to devise Icons that work in the standard 13th Age way for the Zendikar world.
A bit of background explanation is needed to understand why. Then I'm going to basically propose some "models" and see what you guys in the community think about this.
BACKGROUND: Why Zendikar lacks world-shaping NPCs.
First and foremost, we would be tempted to cut the matter short by stating that Zendikar has never meant to be role-played into. As all Magic: The Gathering worlds/planes, it's just meant to be a backdrop to battles that involve tapping the magical resources that are embedded into the world's lands (and this is also the focus of Zendikar compared to other MtG worlds), and havng creatures and spells summoned in this way.
But Zendikar has everything it needs to be at least a common D&D setting. It has dunegons, it has adventurers, it has sorts of guilds of adventurers, and it has all manner of artifacts and magical stuff, a strange unfolding prophecy and a culmination into an eldritch apocalypse involving three Chtulhu-like aberrant gods that will devour literally all reality unless they are stopped. (Oops, spoiler!)
So what it lacks is exactly the classical important NPCs/factions that the Dragon Empire of 13th Age has. Or doesn't it? It depends on the scale used to measure their possible equivalents in Zendikar
LARGE SCALE ICONS: Zendikar doesn't lack big players, but can they be Icons?
The three apocalypse-igniting alien gods trapped within the very earth of Zendikar are immensely powerful.
The triads of gods that the major religious races (Merfolk and Kor) have in their theologies, are just cargo-cult versions of the long-forgotten appearance of the three mentioned world-enders. That is, technically the "true gods" of Zendikar don't even exist: they are historians' failures in keeping the memories of those old terrors for what the truly were. BUT. But... There still are clerics of these gods that have powers. And there still is a connection between the true Eldrazi (the names of the alien elder gods) and the "theological illusion" gods. So two routes are possible here: either we consider the religons' gods as some kind of spiritual avatar of the imprisoned Eldrazi, maybe become so thanks to the mortals veneration, or we even think that while inspired from the Eldrazi in origin, these gods also became something "kind of real" as separate mystical entities.
In any case, we're still talking of distant entities, in all senses.
And that's the problem with the large-scale players of Zendikar: be them imprisoned, mystical avatars of the imprisoned that became somewhat stand-alone gods, or very abstract deities, they lack a lot of the characteristics required by icons.