I do like Civ6 as it is now. Love the district concept and was not fond of the stacks of doom. However, when I first read about the “support stacking” of Civ6 I thought we would get something like the Call to Power II system (or even something like Fallen Enchantress or Endless Legend). I like the concept of building an army and having different “corps” inside it (infantry, cavalry, artillery).
I also like the diplomacy system of BE:RT and the BE concept of settler-outpost-city
Support stacking: While in game now it can be underwhelming, the fundamental system as it stands I think allows you to do almost anything if you are willing to be creative. For example, in the modern combat, one could imagine having antitank crews and machine guns as support units you attach to main combat troops. Add in antiair units, supply convoys, drones, etc, and you have a lot of depth in the system - especially if you balance unit maintenance so that premier support units are harder for cash strapped warmongers to afford!
And obviously you could extend that back through the ages beyond the simple siege equipment we have now. Portable shield walls/ mantlets, contingents of specialized units (imagine the incendiaries promotion for archers actually becomes a special support unit) and so on. It's a great base system combined with corps/armies, in terms of potential. Far superior to doom stacks or limited stack concepts, IMO.
BERT diplo: I liked diplo capital and how you had "ability trees" for leaders. Some were unbalanced as heck, but it was fun because your domestic game played different depending on who you were facing (rather than just who you were playing as!)
It would be neat to have internal uses of diplo capital in Civ6 too.
Settler-outpost-city: The outpost stage was something I enjoyed, and i think the concept could be a good method of integrating things like starting overseas colonies, or having pseudo settlements in the frontier you could pick up or interact with.
One thing I really miss from BERT was how they had a project to convert production into anything; food, gold, science, culture, you name it. Then combo that with Al-Falah and get like 62.5% conversion efficiency
