I like the idea - since plated chargers were nerfed.
Yup, though it would be a class of a horse on its own.
Important is its extremely low speed, good maneuvre and no bump abilities.
Lances on these horses will be mostly useless it is strictly for 1h cav use, no bump also means no bump slashing.
It just needs to be very VERY tanky, otherwise itll be Just be point fodder like the current horses are in c-rpg when they get close. The enemys should be actively trying to hit the rider instead of ganking the horse in 2 seconds.
Keep in mind, that this is truly a shit ton of armor... But these horses will be made to take hits, otherwise melee cavving wont work.