This worked for Aela and Mjoll (spouses) on my game (all 5 remade saves):
1. Trade armor stronger than NPCs defaults (well enchanted helps) to spouse.
2. Ask to see what they have for sale. As long as they equip the armor you just gave them, theyll have their default armor for sale, so buy it.
3. Trade back your armor you gave them during step 1 and trade IE tavern clothes to them. They will equip it.
Take note; They might need to follow you through a cell transition for their defaults to show up in their sell list. Also, this works on weapons and accessories.
This was done on an Xbox before and after downloading Dawnstar and during the latest patch. Has not been tested on non spousal followers YET, and when not following you, they will be naked (undergarments) when entering the cell (home or where they live) - can be fixed by trading a piece of armor from and back to the follower, which forces a full equip.
This happens because they try to equip their defaults when they are loaded for the first time while not following. Don't worry, this won't happen again until they stop following you and are loaded in their home cell the next time.
