Also, Rezaf and I will have to agree to disagree about this, but I think Corps/Armies are paving the way to a compromise mini-stack which has the potential to help the AI, too.
I actually agree that it might "pave the way" somehow, but as of now, corps and armies still are no stacks. Also, I don't see how allowing mini-stacks would solve anything.
Anyway, if I were to make the calls on the Civ6 team and obligated to stick with 1UPT, I'd actually just drop the corps name and just use armies, functionally working exactly as it is implemented right now. When the game starts, your armies can only have one unit, later on three units are max. For the player.
For every level of difficulty above prince, I'd allow AI armies to have one extra unit (and strongly encourage the AI to make use of this).
In other words, on deity, ancient player armies would be 1 unit strong, ancient AI armies 5 units. Combining that many units would reduce clutter, make maneuvering easier for the AI and also give weight to the production bonus of those higher difficulties when it now just fizzles out.
As for 1UPT in general - I LIKE it, but in games like Panzer General etc. - it's just that I feel it has no place in a global strategy game.
UNLESS the scale of tile vs. city was changed dramatically so movement ranges of 10 even in ancient times would be commonplace amongst units on foot. See Warlock.
Even then, moving around all those units individually is just a lot of annoying busywork and traffic jams are bound to be a regular occurance.
1UPT is much more tactical and involved, no doubt about it, but in a game like Civ, it's as bad a fit as whenever two units clashed, you'd zoom in all the way and duke it out 1 vs 1 in the style of a first person shooter.