Blizzard has hotfixed the “Triple Threat” title on live servers, meaning players won’t need to wait until Patch 11.1.7 drops to get it.
How to Earn the Title?
To earn the title, players must complete all seasonal Mythic+ dungeons at keystone level 10 or higher, within the time limit,, in all three roles: tank, healer, and damage dealer.
As you can see below, 
The Enterprising Dungeon Master achievement has three requirements:
The Enterprising Tank – As a Tank, complete all seasonal dungeons at Mythic Keystone level 10 or higher within the time limit during The War Within Season 2.
The Enterprising Healer – As a Healer, complete all seasonal dungeons at Mythic Keystone level 10 or higher within the time limit during The War Within Season 2.
The Enterprising Damage Dealer – As a Damage Dealer, complete all seasonal dungeons at Mythic Keystone level 10 or higher within the time limit during The War Within Season 2.
