Endless Legend 2/Endless Deep

A tall idea incoming, possibly viable on the extremely long run.

A possible sequel for Endless Legend might explore Auriga between EL (thawing before collapse) and ES2 (lifeless, frozen wasteland). In this period, the surface is already uninhabitable, so the survivors go underground, trying to survive in the various caverns/tunnels/laboratories left behind by the Endless. The gameplay would be much like EL, but the playing-field is restricted by the cavernous nature of the environment (tunnels crossing each other at various points). As the game progresses, other tunnels/caverns will become available for expansion and exploitation. The new parts might be accessible horizontally (the game stays in a single plane), or vertically (multiple layers, each one deeper than the other, accessible via previously existing, or buildable lifts). Some factions might be successors from EL (Vaulters, Drakken etc.), some new. (By doing the Vaulter questline we might get to know, how did the second wave of them leave Auriga, to join up with Zolya and her people in ES2). The player would have to deal with the other factions, the underground environment and the beings dwelling in the dark (you thought that you have left the Dungeon of the Endless behind, didn't you?). The general aesthetic of the game might center around the early industrial age (Dust-powered muskets), and the endgame might feature bolt-action rifles. Of course, everything would be in allignment with EL's Dust-centered fantasy-vision.
P.S. It's of course just a humble idea by a fan. Comments are appreciated!