There needs to be a way to outfit your sovereign with the new equipment you research. I find it strange that I can outfit a simple commoner with plate armor, and magical rings, but the leader of my kingdom has to rummage through ruins to find items for himself.
I know you can trade these extra items between units, but as far as I can tell you cannot un-equip the armor from a trained unit and transfer it to your sovereign. And were that possible, it should still be possible to take your sovereign into town and create items and equip him with any equipment you've researched.
Hopefully this is already in the works, and simply not in the current build.