Assassin's Creed: Odyssey - 9 Future Settings Ubisoft Must Use
6. The Crusades
Total War: Rome 2 came about when Creative Assembly realized they were running out of ideas for their historical franchise. They turned back to their classic Rome: Total War, and made a second. It proved to be a good idea - they took mechanics they'd developed since the original and implemented them, and it clearly spurred their imagination to make many new games.
Ubisoft could do the same. The original Assassin’s Creed hasn’t stood the test of time - it's been a good ten years since it was released; graphics and gameplay standards have changed hugely in that time. By taking the series back to the Crusades, they could reinvigorate this historical period by bringing all the new gameplay features that've been added to the series since the first.
In addition the Crusades extended far beyond what we saw in the first game, in particular the lands between the cities were glorified loading screens and there wasn't as much interaction with the human side of the period than there are in most Assassin's Creed games.
This would, in effect, be a remake though. Ubisoft would need to play it safe if they were to essentially remake the first game.