Sounds like a good list, Tyrant. I never really thought of #2, but I agree.
#4: Especially a leader queue and a way to enque more than 1 unit per click.
#7: Great in practice, bad in theory (the opposite of most cases
In other words, strict teams would be loads of fun, but The Son of the Sun teaming with a Frost Giant aganst the Prince of Death and Virtue is conceptually pretty silly
More diplomacy optinions are always good, though, regardless of what you have to do to rationalize it.
#9: Yes! I was about to send my rainbow pretender underwater as support, but then I realized... he had no spells he could cast underwater
It's a bit annoying, too, that there is no good script you can put on an amphibious water mage that will work above and below water.
#12: I'd just settle for a 25-slot Hall of Fame
But sub-heroes are an interesting idea. Like "Big-fisted Bob" or "Hank, the thief that usually escapes".
#14: Totally agree. I've been advocating a 5-point scale rather than a 3-point scale for a while... 4 usable points, and an fifth reserved for e.g. a Cold 4 nation that gets hit by Wolven Winter. A couple more balances might be nice. What would they be... fiestiness/meekness, giving stat bonii and malii to national recruits... and science/superstition, balancing unit resource, gold costs, and leadership versus undead and magical leadership, the probability of getting random magic picks and extras levels on mages, and extra preaching effectiveness.
A science/superstition scale that adjusted weapon and armor strength, and bow range of the nation's troops would also be neat, but a +-3 swing on protection and damage would be pretty severe. If only Illwinter went floating-point, it would be possible....