In terms of crossover events nobody asked for, we would be fairly confident in saying that marrying the mechanics and design of Civilization with the setting of Games Workshop's 40K universe would be pretty high up on the list. We would happily defend that position until Cadia blows up (again), but that hasn't stopped Warhammer 40,000: Gladius - Relics of War from turning into a pretty decent 4X game so we're also happy to stand corrected.
Part of its success is how Proxy Studios has been allowed to tap into the wider 40K lore. The game launched with only a handful of factions, but has since steadily deployed add-ons for the other races, such as Necrons, T'au and even Tyranids. This latter addition has been one of the best adaptations of that iconic race into videogame form we've ever seen, as it happens. Next on the roster to deploy to Gladius is the Eldar, or Craftworld Aeldari as they are known now in today's more copyright-friendly vision of the grimdark.
Launching on November 12, The Aeldari will have 19 unique units, as well as bespoke mechanics that will set them apart from the other races fighting for control of the planet's surface. This faction will be able to exploit webway gates in order to move about the battlefield more quickly, and many of their units can move even after using all of their actions.
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Warhammer 40,000: Gladius - Relics of War puts a hex-based 4X spin on the setting