The mods can move this topic to a more suitable forum if there is one; I didn't see a wishful thinking category, unfortunately, but does anyone else think this would be a fun addition to the game?
Think about it: getting good gear for companions is presently 100% dependent on RNG, whether it's your own or that of another player who is listing companion gear on a trader. And there is no way at the moment of getting better than purple-quality gear for our companions.
I know that a companion is not a replacement for a player in terms of survivability, DPS, etc. But I think most of us enjoy playing with our companions, aside from maybe Bastian... I personally wouldn't mind grinding for leads for an artifact weapon or armor/jewelry piece that only my companion can equip. And since they're mythics and your companion can only equip one of them at a time, it's not as if they should radically throw off game balance or anything - particularly if the perks of equipping one are balanced by some disadvantage, like how most mythics work for players.
I bet they could add an interesting dimension to gameplay, if done well. And ESO can even throw in a little achievement for equipping a mythic piece on a companion for the first time!