This is something that’s in my head noggin for a while, so allow me to explain this idea. A Mission table, but your followers are your other characters.
You make your alts (or you can use your main too), level them up as you would, and they will be available to your Character that your playing as a follower, the same way you could with your Previous followers. For the Calculations of the percent of success on missions with your Alts, it doesn’t need to be too complicated, just take Ilvl, Level (if they aren’t max level or below the mission’s level requirement) and assigned certain counters to whatever the Class/Spec that Alt is. Say for example, Assassin Rogues Counters Ranged Troops, and ranged troops reduce mission success, so countering that means an increase in Mission Success.
“So we send our Alts to do missions for the character were on and that Character is gonna be unavailable to play until the mission is done?”
Well… this where i come forth with this another little twist with this one. This mission table will gives you two options to carry out the mission: You can do the same way you did on previous itterations, and just set it and forget it, Or… a more hands on approach where you can send it to the character and when you hop on that character, it acts like a personal quest to take from your Alts.
An owl/pet/companion etc whatever fits the Questgiver’s class will come to you to accept the quest, Also acting as a turn in when you complete said quest.
“How would the Rewards be divved up?”
Well the traditional option will only reward the “Questgiver” Character 100% of their rewards, but the questgiving option will reward 50 - 75% (depending on the difficulty of said mission/quest) of the reward to the “Questaker” character, while the Questgiver Character gets 75 - 100% of the reward.
And Yes, Warmode bonuses apply in this option as well.
“How about the Rewards themselves?”
Well, it be the usual sort, Gold, BoE Cosmetic Gear, Resources, Rep, Pet charms, But also include Useful BOA Gear for your alts, Materials, Mounts, Toys, Pets and Upgrades for your Pets, Profession related Recipes or things that could be useful for you like Gems to socket, enchants or potions, Reputation rewards, Quest items, and even sometimes, even a box containing something (anything) from an old dungeon or raid, or maybe even very rarely, a box from the BMAH containing one item. I would say Gear from the current expansion, but they always tend to be on the same level as normal/heroic raids, so i’l just leave that out.
“How difficult would the Quests they be for our alts?”
Well to give you an idea, if it’s a quest to kill a boss, and you go solo it, it would be a Heroic Dungeon boss level to Mythic+ 15 Dungeon Boss level, and maybe even Mage tower levels. For click to gather quests, Gathering will be 1 second slower and will attract other mobs who might be guarding it and try to attempt to steal it back from you with a 5 - 1 second interruptible cast, and when you die to the items, you might lose a 15% of the items you collected.
And quests themselves will be timed. I would imagine it will be like 4-8 hours minimum, plenty of time to go though the alts, and plenty of room for trial and error. Also, no the mission counters wouldn’t apply here, so you wouldn’t have to worry about accidentally making the timer shorter for yourself. It’s simply there to add urgency to your character. If you do happen to complete the quest and still have a lot of time left, the compainion/pet/owl, etc will come over, and allow you to turn it in, which also in turn counts as a success for the questgiver. if you run out of time, you fail the quest, and the questgiver’s mission fails.
In addition, the mission table will also show the questtaker’s current location for preparation purposes.
“What if i want to do the said quests in a group?”
You can do that, you can also solo them if you want as well, it would just be harder that way.
“What sense does this make in lore?”
…Your character happened to know some mercenary for hire they might have come across in there adventures offscreen?.. 
But that’s my idea, i’m open for feedback, ideas, opinions, so on.
Edit:
Aimbot has definitionally brought up a good point and it allowed me think about what should those people get if they want a more passive approach, but don’t want to necessary use their character. I’l quote that idea i have explained, though before we dive in, it’s important to know that i framed the idea as in a way to be a bit more active in the game (or playing the game if you will) then passively waiting.