The main focus of Gatecrash is, of course, the five guilds that re-debuted in the set. However, one minor aspect of the set that was touted quite a bit had more to do with worldbuilding and flavor than mechanics: The emergence of Merfolk on Ravnica. The creature type had not been seen on the city-plane before, and it was assumed that they were simply not present there, but the backstory of the reformed Simic guild has revealed that they were in hiding all along in Ravnica's vast underground oceans. But for all of the hype, only three Merfolk actually appeared in Gatecrash, all of them linked to the Simic guild in some way: guildmaster Prime Speaker Zegana, Merfolk of the Depths, and Simic Fluxmage. Hardly a massive force of sea-dwellers.
This begs the question: Was R&D foreshadowing something in Dragon's Maze and beyond? It's worth nothing that not only are all of Gatecrash's Merfolk aligned with the Simic Combine, two of the three are both green and blue. This idea of a green-blue Merfolk sounds strangely familiar; specifically, it brings the planeswalker Kiora Atua to mind. Kiora has been a known quantity since 2011, with Duels of the Planeswalkers 2012. She's known only to be a green and blue-magic-wielding Merfolk who specializes in ocean magic and sea creature summoning. Of course, we can't feasibly see her as a planeswalker card in Dragon's Maze, since her compatriot from Duels 2012 - Ral Zarek - is going to be featured in the set, and she shares the blue part of her color affiliation with him.
But that doesn't mean Kiora can't have any presence in the set. It would be interesting if her character were teased to the audience through cards named after and flavored around her in order to generate excitement about her appearance in a future set. For example, we might see something like:
Kiora's Deepseer 1GU
Creature - Merfolk Wizard (Rare)
1GU, Tap: Search your library for a Kraken, Leviathan, Octopus, or Serpent card, reveal it, and put it into your hand. Then shuffle your library.
Kiora's interest in massive ocean monsters certainly synergizes well with the themes of the Simic Combine - large creatures are good for triggering evolve, for example.