Since our raid team (CthUwU) only has 5 mail players and we didn't want to separate each other in order to funnel gear better, we decided to try out no-tanking every dungeon. We actually ended up successfully completing every dungeon on Mythic with no tank and only mail characters. The players were me: Fawnstalker, Bigempct, Glocktrain, Shargle, and Milky.
We used 3 Hunters and 2 Shamans, one of which was Resto. The hunters swapped between MM and BM depending on the burstiness needed for bosses or the tankiness needed via our good pal Clefthoof.
Earth elementals, pets, and our poor elemental shaman ended up tanking most of the time. The only boss we had trouble on were Mueh'zala because pets don't count as a melee-range player, which causes Crush. Every other boss was killed in around a minute since we were 4 dpsing. You can see in logs how we did this.
We all thought it was kind of impossible and a joke, but tried it anyway because we wanted to 5 mail funnel instead of start 2 separate pugging groups. We're glad it turned out that way, because we got some awesome fun out of it. The trash is arguably harder than the bosses, but it got to a point where it didn't feel that different from normal Mythics. Misdirect played a huge part in the runs.