The biggest thing I want is for late game actually matter. I find it ridiculous how you can cruise through the industrial-future eras without building factories (or IZs), research labs, broadcast towers, sewers, power, railroads - the list goes on. In my opinion you should get absolutely pummeled in the late game if you neglect to build modern infrastructure. For this to happen, these key things must be changed:
1. Major buff to all tier 2 and tier 3 district buildings with the exception of the university.
2. Major buff to benefits from power and/or big penalties for lack of it (Also nerf the coal plant plz)
3. Slowdown tech and culture in the late game
4. Major nerf to late game chopping
5. Nerf faith/gold buying and/or accumulation
My second biggest wish is to curtail ICS strats. I hesitate about "nerfing wide and buffing tall" because I don't want to end up with civ V which I absolutely hated. I feel fighting for territory, especially in the early game, is essential to civ, and I'm glad that aspect is back in civ6. I also believe 10 size 10 cities should always be better than 5 size 10 cities, and that 10 size 10 cities should always be better than 10 size 5 cities. Nevertheless, large cities kind of suck right now (10 size 5 cities is almost always preferable to 5 size 10 cities) as your better off spamming smaller cities as close as possible across the map. My suggestions to curtail this:
1. Buff specialists - specialist outputs need to be able to compete with working tiles. Also have higher tier buildings give more specialist slots.
2. Tie buildings to population size. For example, you need 5 population for a library, 10 for a university, and 15 for a research lab.
3. Make amenities easier to come by - simplest solution is just to buff the EC/WP buildings, but I wouldn't mind seeing them bring back civ2 elvis' (entertainer specialist).
As for cosmetics, I wish the districts blended into each other better. Districts were a really cool idea for how your cities would grow and evolve overtime, but they just look like a bunch of disparate entities right now. I wish they blended in with the city center and each other to create the look of a single city spanning multiple hexes. On another note, railroads blend really poorly into districts as well. Admittedly, this probably is more dlc/expansion than patch.
Other random thoughts:
-Make global warming change plains to desert, grassland to plains.
-Buff anti-cavalry or nerf early game cavalry