Would Ivory still be a luxury resource or would they change it to where Elephants become a strategic resource? Alternatively Ivory could go to a walrus resource but that might be more rare if they only would appear in tundra/snow tiles.
If it does turn into a luxury that can be used like a strategic resource it sounds like it could cause some problems due to the new GS resource mechanics, unless I'm not seeing something.
With the current Civ VI Resource System of rigidly differentiated Resources, making Ivory a Strategic resource would probably preclude it as a Luxury Resource. I think that the rigid differentiation is Hard Coded in some way - one of the Mod/Coder Community could say for sure: I know there are Mods that add Resources, but I don't think I've seen any that change the Class or Type of any Resource.
One possibility would be to change Ivory to either Walrus (a Coastal Tile Resource) or Frozen Mammoth (Tundra, Ice Resource) - Siberian Mammoth tusks were a major source of ivory in the 19th century, at least.
That would change the map dynamics of Luxury Resources, but not severely: there are several other Luxuries like Silk, Dyes or Spices that use similar terrain/climate tiles to what Ivory appears in now, so there wouldn't be any major degrading of access to Luxuries.
The really tricky part, because Start Location Preferences are so badly coded in the game (9 starting attempts with Nubia without a single Desert tile of any kind within a starting radius: 'nuff said) that requiring Ivory for a UU would in some or most games preclude getting the UU at all. As posted, a 'quick fix' might be to not require a Resource for the UU, which is not unknown in the Civ games.
Finally, just a note on the 'uses' of Elephants, some of which I posted earlier:
1. Heavy Cavalry-Type 'Melee' Unit - as used by Carthage, Seleucids, Ptolemies, with an Anti-Cavalry Bonus because horses not used to them are Absolutely Terrified of elephants.
2. Ranged Unit using elephant-mounted archers, as used by most of the Classical Indian states, Khmer, Burma. Could justify giving a slight Boost to the ranged fire, because the archers have a noticeable height advantage over even horse-mounted foes.
3. Siege Unit or a Siege 'Boost' in using Elephants to push in weak walls or gates, as used by the Ptolemies. This might better be a Promotion in a specialized Pachyderm Promotion Tree.
4. Medieval/Renaissance Ranged Unit mounting muskets, very light cannon, or catapults on elephants, as done by Siam, Mughuls, Gazhnavids, and Khmer. At this point, though, the Elephant is becoming marginal as a combat unit: too big a target, too smart to want to get shot at twice. On the other hand:
5. Elephants as cargo/supply animals. During WWII a lot of supplies were carried over the 'Hump' - the mountain roads between Burma and China - on elephant back, and elephants were used to haul heavy artillery in India and Southeast Asia. When the Elephant Combat Units become 'obsolete', access to Pachydermic Traction in the Renaissance/Industrial Era could still provide extra mobility for Bombards or Field Cannon: perhaps allow them to ignore movement restrictions on Hills.