What is this Mythic and AP farm thing going on?
Prolly the key boost thing.
4 highly geared people form a group, advertise as: "Bring your +2/+3 key and we get you 3 bonus chests". You join, provide your mythic key, they flatten the dungeon for you, everyone gets bonus chests with potential loot and guaranteed AP items (a few thousand).
Then they say goodbye to you and find someone else.
Now, here's where this breaks the gear chain and will generally bring down the nerf bat: this week those 4 people can boost +2/+3 keys. In a week? 2 weeks? they'll be overgeared and can boost +4. What will they be boosting in a month? So they're essentially injecting ever escalating levels of gear into the ecosystem (you as the fifth member get whatever they get, so as long as you provide a key you will be getting better and better gear each week for simply pitching up).
It gets even better when you realise that the key is not expended per use. A +2 turns into a +5 if properly used, so in a month when people are boosting +5 keys you can essentially get _3_ free loot injections on each of your characters: the +2 they boosted, the resulting +5 they boosted, and then the resulting end of the week grand chest you get from your order hall.
Only real reason to do raids will be to get tier tokens, I guess?