I have something that might not count as a minor request...
I play as the Hippus sometimes, and I hardly ever get level six melee units, but i have plenty of horsemen/horse archers/chariots that are level six. I think someone should make a new unit - an immortal replacement - that upgrades from chariots and horse archers. You might have to raise the level requirements for it - to say, level 7 or 8, but it would be able to fortify, wield weapons, etc. It could be called a Battlemount or Charger... It would be very awesome if someone could do that.
I'd like to give the Hippus Mounted Immortals too, but ,you see, the problem is that individual units are set to upgrade to various unitclasses, so in order to let the Hippus upgrade their mounted units to Immortals instead of their Melee units you would have to give them UUs
both for the mounted units you want to give this ability and for their Champions.
Well, actually there are a few ways you could get around that. You could make it so that the only way to upgrade to an Immortal is through a spell, which could be civ and unitcombat dependent. There are numerous problems with that though. First, the AI probably would have trouble understanding it. Second, in order to not make upgrading a horseman or a knight cost the same you would need to either have a different spell for each unit or pay the cost in python. Most importantly, limiting it to 4 at a time would require a python prereq that would be called way too often and would slow the game way down, at least after Divine Essense was researched.
Another way to handle it would be to take a page from the Mercurians and not have these Immortals be Immortal UUs at all, but seperate unitclasses. That way, all civs could have their Horsemen upgrade to Mounted Immortals, but every civ but the Hippus would just happen to have NONE as their Mounted Immortal UU and the Hippus would have NONE as their Immortal UU. The downside here is that Tolerant/Conquerer trait leaders could get access to the different unitclasses of immortals and thus get a least twice as many immortal units as other leaders. That sounds unbalanced.
Of course, it would be simple to give civs Immortal UUs that don't match the unitcombat of the units from which they upgraded. It may be harder for the Hippus to get melee units up to a high enough level, but it would be worth it if you get a fast, mounted, CRIII immortal.