I wasn't picturing magic instead of armor; rather of how magic would be used to reinforce armor. Rather than just a spell cast over the whole thing, I was envisioning having to do as much work in the spellcraft as in the metalcraft.
You mean embedding magic into armour during the forging process? Then you would still have just the usual pieces of armour, just reinforced.
Tolkien did something similar to that with Daggers of Westernesse, which was then copied by George Martin for his Valyrian Steel.