The corps option of limited stacking in CVI, I'm definitely looking forward to seeing how that works. Districts are going to be fun to mess around with as well, both because it won't become mandatory for me to put cities at the coast if harbor districts are a thing, and pillaging might actually be more meaningful if districts are more important than plain old improvements.
I personally prefer 1UPT over stacks of doom forever, but a variety of problems makes it a pain in the arse to use melee units in CiV.
1. There's a lot of dense terrain that slows your units down. Map choice can end up generating a lot of choke points all over the map as well.
2. Most melee units in the game only have 2 movement points. Combined with the dense terrain, your melee units could potentially be moving 1 tile per turn. That is really bad.
3. Building roads to increase the throughput of your army starts getting really expensive gold wise, which already sucks since unit maintenance costs scale very strongly.
4. Cities are really hard to kill and have a strong counter-attack.
Contrast this with ranged units, which
a. Can attack from 2 (or more!) spaces away, granting all sorts of initiative and the ability to focus fire more effectively.
b. Can attack without worrying about counter-attacks, and even counter-attack against melee attacks.
c. Generally don't cost that much in hammers or gold over their melee counterparts.
d. Can't capture cities! But oh boy, they're way better at actually fighting cities than melee units are.
I remember a few articles a long time ago about CiV taking some inspiration from Advance Wars (it was one of the reasons they went to 1UPT). But even in AW, units didn't always move at glacial speeds, and there was still a limited stacking option instead of disallowing stacking outright. General map design usually avoided making choke points all over the map, and didn't cover like >50% of the map in mountains and forests.