As I've said before here, I suspect that there is still some sort of content or even another expansion or Season Pass, of only because of certain gaps in the unit progression (Mustketman straight to Infantry, Cold War Bombers serving as "Stealth" Bombers) and because some of the most notable Leaders associated with previous Civ games (Napoleon, Nobunaga, Julius/Augustus Caesar, Attila, Pocatello/Hiawatha, Bismarck, Washington/Lincoln, etc.) would seem to lend themselves toward a military-centric themed set of content. Maybe it will happen, maybe not, but as much content as there already is for Civ VI, it still feels like some pieces are missing. That said, I'll happily support either more content for Civ VI or enjoy it while we anxiously wait for Civ VII.
If and when Firaxis does move on to Civ VII, I do have a personal Wish List (assuming most/all of the core features of Civ VI, such as Districts, carry over):
1) A return of Leader animations more like Civ V's, where they are human beings instead of caricatures, and they're surrounded by the architecture/environments they're associated with instead of a stark, static, and depressing black backdrop.
2) Maps that lean more toward Civ V's realistic aesthetic than Civ VI's more animated look. Don't get me wrong, Civ VI is a very pretty game as is, but (Civ V map mod aside), I really miss that more natural look to the topography.
3) I'd personally rather that Firaxis stick strictly to semi-historical relevance the next time around. Zombies, vampires, mythological figures, Rock Bands, and post-apocalyptic modes have felt like personal indulgences on the part of the development team. While I've dabbled with some of them, they just don't hold my interest and detract from the core theme of the game, at least for me personally. I'd rather that time and effort be put into actual Civs, Leaders, Wonders, and core game mechanics refinements.
4) Make mods available to console players as well as PC players in some form or fashion.
5) The ability to select either the "Unknown Regions" map aesthetic or the white clouds of previous games for unexplored territory. While it seems to have improved over time, all of that uninterrupted brown sometimes makes it difficult to discern key details of explored territory in Civ VI.
6) Alternate Leaders that actually play differently (such as how Napoleon would differ from Catherine de Medicci).