Would you be willing to create a Dragon Rider type unit similar to the Phoenix mounted units in the Phoenix Legion mod? Dragon Princes riding actual Dragons for Tier 5? Perhaps with a hard cap so it cannot be spammed?

Yes, but i don't know how i could set them a part from normal dragons since they would be just that but with a rider.

Well with the rider you could make it have better stats over the Dragon counterpart, but for balance they could be hard capped so you could not spam them so the Dragons would still be in use. Perhaps give them an ability as well.

Perhaps at Tier 4 you can be allowed 1 Dragon Prince on Sun Dragon and at Tier 5 allow 1 Dragon Prince on Moon Dragon, or something along those lines. Hardcapped at 1 per individual building in each province it would be a nice way to round off the Legion.

Something akin to the Knights of Tor Gaval for the Legion.

I could make them similar to the Knights of Tor Gaval, mounted on smaller dragons but have 4 units instead of aone dragon that's just stronger.

Hey I just wanted to say this is my favorite mod for the game, I was wondering if its possible to make a hero version for this mod

A hero version? You mean like adding a new hero?