1.As of now there are 2 heraldic armours so, why not add another, "Plate with Heraldic Surcoat/Tabard/Whateveritscalled"
It would have the same stats as plate, the non-heavy one, and have a decent look.
2. Customizeable "Rear Horse" key, at the moment to rear your horse you have to (ctrl+j) this wouldn't be a large buff or nerf to cav because stopping can help them avoid Pikes etc, but can also make them vulnerable to missiles.
3.Pike Bracing, simaler to Bayonet bracing in Napoleonic Wars, though with a longer weapon, making pikes/longspears useful against cav.