Ubisoft reuse engines a lot, Prince of Persia for example ran off the Jade engine, which was named the Jade engine because it was developed for Beyond Good and Evil. This teaser, if it's real time which is possible, is probably running off the Scimitar engine, first used in Assassin's Creed. This is why it probably looks a little blah and bland.
Of course it could also have something to do with the fact that Hillys has completely dried up and is no longer the lush planet it was. Game about saving the environment? Awesome.
Then it wouldn't be so much about SAVING the environment as learning how to live with the consequences (which, honestly, is what we should start doing right now).
Anyways, theres no reason why it couldn't be Hyllis, sans environmental disaster. We're a water planet, but the middle of Arizona is a helluva lot different than Venice, for example.