1. A balance pass for pantheons / beliefs. The best pantheons are, unsurprisingly, always the best ones. I get that because many of them are resource-based it's difficult to balance them since many of them are situationally powerful, but the strongest ones that don't have conditional terrain/resource requirements could be toned down a bit. Ideally the nonconditionals would be reliable if you don't have many of any one resource/terrain, but at the moment unless you have obscene amounts of luxuries or some other resource the respective pantheons are lackluster.
2. Harder Eurekas/Inspirations. As many have said, they're a bit too easy to obtain through normal play. They could be strengthened to compensate, but they should not be easy enough to obtain as a side-project while focusing something else; rather, they should be something along the way of whatever you're already focusing. Founding a coastal city for sailing is a good one; you might not aim for that Eureka unless you already want a coastal city or are planning one in the near future.
3. Related to above, slower science overall. Even the AI on prince is reaching the modern era hundreds of years early--alternatively, if the science rate is too drastic to change, just adjust the pace of the in-game years. I can accept faster science to speed up gameplay, but the year counter should at least match up roughly with tech eras at lower levels of play; it's simple, but helps a lot with flavor and immersion.
4. Chopping nerf. I personally have never chopped woods for production in any game of Civ VI, but I don't want the feature to go away because it makes sense from a historical perspective. Gameplay-wise though, it's currently incredibly strong and only looks to be getting stronger in VI with the governor that boosts it. It could use some tweaking.
5. District adjustments. CHs and Harbors were at least looked at already, but Theater Squares could use some touching up as well; they do fine for holding Great Works but a bit more leniency with adjacency bonuses would make them more viable early game. More variability in district choice is nice for gameplay, and flavorwise once your discover Drama and Poetry and the like it does make sense that you'd at least have a few TSs. IZs could be boosted a hair too, but overall they're alright in the later game.
6. Trade routes giving something to the receiving city. It doesn't have to be huge, but at the moment making your cities ideal for trade routes isn't very rewarding. You get roads to travel on and traders to pillage, but even then those same roads could be used to go into your city. There's also the fact that other civs are somewhat economically reliant on you if you're a main trade destination, but that's an indirect bonus that doesn't feel like much during actual gameplay. Even something superficial like a bit of gold at least presents something tangible to say "this city is the heart of trade".
7. AI adjustments. There are a lot of tiny things that added together make it leave a far worst taste in the mouth than it should. Most glaringly, joint wars should be looked at so that they make a bit more sense on the player's side. Sure, behind the scenes your ally may have been offered enough to declare war against you, but that doesn't stop it from feeling unwarranted and arbitrary. Less nagging with deals that you've already declined would be nice too.
8. The ability to ask an ally to declare war once you've been declared war on. Seriously, I'm not sure how this isn't already an option. This might be the military alliance in RnF, hopefully.
9. UI changes. Not much to say that hasn't been said already. They're not really balance changes, but they improve QoL enough to be a top priority, IMO.
10. Auto-selecting the search bar when opening the Civilopedia. Please. I know it's technically also a UI change but I really just want to emphasize this thing especially. 99% of the time when you open the Civilopedia, you're not just planning on staring at the welcome page.
I really like Civ VI's new ideas and gameplay, and am hoping that RnF polishes up the implementations of these ideas and improves on the lackluster aspects of gameplay. Fingers crossed.
No one flies helicopters across the ocean (DO THEY?!?!)
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