On the elephants.... I was thinking about using a building called a "Khedda" - buildable only in a city with a worked source of Ivory. It would create say, 2 (?) of a new strategic resource called "elephants." Those elephants would be required to build elephant units, similar to the way we set up Camels. This at least ties these units to a resource on the map, even if the Ivory (luxury) has been traded away, there are still enough elephants remaining to use for units.
Looking at the available artwork (including all the UC mods): there are 3 basic elephant models in BNW/DLC: Naresuan (Indian, rider with spear), War Elephant (Siamese, rider with bow), African Forest (Carthaginian, "castle" with spears). Can probably recolor these to give them a completely different appearance.
Have also found two other models: Woolly Mammoth (no rider, maybe an earlier unit I can add a human "Kumki", or herder), and the Ballista Elephant (rider with large horizontal bow).
This makes 5 basic elephant models to use. I can also add other models (like figures from Swordsman and/or Spearman units) into the basic elephant model to create a new, composite model. It changes the overall appearance and makes them look less like a copy of the original. Could even through in some lions, tigers, bears, wolves, dinosaurs, eagles, and ravens if you really wanted to mix things up...
So, there are more choices for elephant units than the camel models, since we only had 2 of them. No need to use them all, just the most appropriate. Just spitballing right now, but for starters, how about a "class" of 4 units:
1. Mammoth with Kumki (Animal Husbandry/Ancient): slow (move=1), but powerful melee attack. Minor Fearsome Elephant promotion (10% bonus).
2. Naresuan (bow. Horseback Riding/Classical): normal speed (move=2), ranged attack of 1? None or few promotions
3. Ballista Elephant (Engineering?/Classical): normal speed (move=2), ranged attack of 2, siege bonus vs. cities
4. War Elephant (based on the African Elephant, Physics/Medieval, obsolete at Chemistry): mounted speed (move=4) melee unit - with major Fearsome Elephant (25% bonus) promotion, probably bonus vs. troops in open, etc.
A player would still need the Khedda to provide the elephants to build these. Can also add an "Improved Khedda" to replace the basic Khedda and offer more elephants (maybe 3?), but it helps if we tie that to a specific Technology, say Metal Casting (in the middle between Engineering and Physics).
First draft thoughts, no pride of authorship, so all comments welcomed. Also - if we want to add any other units, e.g. Ghazi, etc., let me know how those would look as well. Thanks.