First of all, a stainless steel moldboard. Not the framework, just the actual "sheet metal". No need to paint it. (I have plans for my plow this summer, got the stainless already)
As Deere John said, bushings and grease fittings where they should be. Especially the center pivot "king bolt". That should use a tapered bearing, like a wheel bearing. It should be a "mini spindle" not a bolt.
No bolts going through metal without a bushing.
A self contained underhood hydraulic system, like Barnes makes (for example). It could serve a dual purpose, work the dump body, and the plow.
A lift cylinder that is interchangeable with the angle cylinders. Then only one spare would be needed, "just in case".
Urethane cutting edge, or a urethane edge, sandwiched between two steel edges. The urethane to support the weight of the blade, and steel to scrape better. Urethane makes for much quieter plowing.
Downpressure system.
Hydraulically controlled plow wings.
A hinged sno foil that can fold back when you don't need it.
A galvanized A frame, as Alan mentioned. Along with the rest of the steel plow framework being galvanized too.
The problem with all of these improvements, is that we'd never buy parts! It has been said that Meyer is in the parts business, but they aren't the only ones. True, other brands may need parts less often, but all plows need parts sooner or later. Anytime you have a bolt holding steel together without bushings, and the bolt is harder than the steel, the steel will wear, causing the holes to oblong.
I have more, but these come to mind right now.....
~Chuck