I've come up with an idea of my own when reading threads about hirelings and combat pets. I like the idea and I'd love to see something similar added to the game in the future so I'm sharing my thoughts with you:
INTRODUCTION
The Adventurer's Apprentice is a NPC that'll help the player in its journey. You are to teach him how to be a good adventurer by taking him/her into the wilderness and killing enemies together. He/she is an adventurer in learning so he/she is
weaker than any other player character on the same level and don't feel confident enough to go into PvP zones, Trials and group dongeons.
UNLOCK THE APPRENTICE
Once you reach level 10, you'll have to complete a certain quest to be able to call your apprentice with a memento like a war horn or something. Then the apprentice will be unlock for that one particular character. If you use the memento on another character who didn't complete the quest, it won't summon the apprentice. He/she will not be the same for every character you have, meaning that you can customize him/her to suit everyone's of your character playstyles and backgrounds if you like to RP.
THE APPRENTICE APPREANCE
You will be able to create your apprentice like you did with your character, but he/she won't belong to a faction and is not taking part in the war. That way, you will be able to re-customized him/her with tokens in the Crown Store. Costumes and polymorphs can be applied to him/her too.
LEVEL AND SKILLS
- Like a mount his/her skills and progression will be bound to the character and will not be account wide, every apprentice is different for every characters.
- The Apprentice scale to your current level, meaning that if you unlock him/her at level 45, he/she will be level 45.
- His/her level has nothing to do with his/her skills. He/she will have a limited amout of abilities and passives compared to a regular player character, in short, the apprentice is a weaker and simplier version of a player character. You will have to kill ennemies to earn your accomplice experience points so that he/she can rank up and gain skill points.
- An apprentice doesn't have any class. By talking to him/her, the apprentice can fulfil the role of a tank, dps or healer. His/her skills will not be the same as player characters, but more like the ones hostile NPC's are using and the skills avalable will depend on the role you set your apprentice on. You can switch the role of your apprentice anytime you want by talking back to him/her.
THE APPRENTICE LIMITATIONS
You cannot have both a vanity pet/assistant and your apprentice summoned. You cannot use the apprentice in PvP zones and group content. When summoned, the apprentice will use one slot in your group. You can gear him/her the way you want, it will affect his global stats but that won't give him/her the weapons and armors skill lines, he/she'll have its own depending of his/her role no matter the armor or weapon he/she is wearing.
LAST WORDS
English is not my native language, so I may have some difficulties to explain myself but I'll try. This is just some ideas, I have no clue if this kind of feature can be added in ESO, but I know there is something similar in FFXIV with the chocobo, so it's not something for single player games only.

Feel free to discuss!
Edited by Neirymn on July 13, 2016 8:44PM