Great idea, I've been thinking of it some time before. It may be named "Frankish Paladin" and the unit can be based on graphics of actual unit Frankish paladin (in scenario editor), or any other mounted hero with lance, you know what Im talking about, right?Cool . A very costly upgrade like ''Royal Paladin'' which would give some small armor or attack bonus to their paladin (or speed bonus).
This would go against the theme of AOC's progessive upgrade costs. Giving the Franks a special 3rd upgrade to the Knight line means it needs to be much more expensive than the Paladin upgrade to follow suit with how AOC's upgrade costs are structured. Meaning something like 2K food and 1.2K gold. The upgrade also needs to be worth it for it to be there.
I think the real problem isnt their paladin, its their versatility. Early eco had already got a big boost with +25% on berries, they just need something to help them counter pikes.
Seriously their paladins are already very strong, making them stronger will be very hard to balance.