@TB - one area of concern is the odds calculation changes. The C2C AI was changed several months ago so that odds used in most places are no longer the odds of victory, but rather the odds of a desirable outcome. As an example consider an attack by a stack of two swordsmen against a stack of two somewhat better units (but not hugely better). The outcome will be that you lose the first swordsman, but win with the second, resulting in a loss of a swordsman for an enemy loss of a better-tan-swordsman. The C2C AI will give this desirability odds of over 50% (because the expected outcome is desirable), whereas the old-style BBAI one will give it less than 50% (because the first attack is expected to fail).
This is implemented by an extra layer CvSelectionGroup::AI_attackOdds(). The original CvUnitAI::attackOdds() just sees the top unit (first combat), but if you instead use group()->AI_AttackOdds() you get a result weighted according to the entire stack combat outcome. Most of the AI now uses the group version.
You've changed the unit version fairly extensively, and since the group version calls the unit version to evaluate each combat in the stack, this is probably ok, but if there are any extra uses of CvUnitAI::AI_attackOdds() you may need to change those to use the group version instead.
I'm also slightly (but I'm not sure it's wrong - just concerns me) concerned about the withdrawal odds calculation changes in CvUnitAI::AI_attackOdds(). The line you overwrote there (necessarily to get the new code in) was itself a change from the BBAI original (as per the comment above it about avoiding stupid suicides), and I'm not sure the new code respects the intent of that change (in which case you might find units with very low odds but some withdrawal capability suiciding a lot again)
Edit - in general its hard for me to evaluate the (code) changes, as I don't have a good understanding of the overall intent, so I'll wait until after you post an overall description for players and modders as you have indicated will be happening soon before I attempt such a review.