Blizzard has confirmed that the new Myth upgrade track coming in Patch 10.1.5 will apply retroactively to gear which started at a base item level of 441 or higher!
Myth Upgrade Gear in Patch 10.1.5Gear which drops at item level 441 or higher by default will now fall in the Myth track. Blizzard has announced that this is indeed retroactivate. This includes gear from Mythic raid, Very Rare items from Heroic raid and Mythic+ Great Vault items.
One additional PTR note for the week:ITEMS AND REWARDSGear created at item level 441 or 444 can now be upgraded using the new Myth upgrade track instead of being above the upgrade system entirely. The Myth track is a new track that goes from 441 (Myth 1/3) to 444 (Myth 2/3) to 447 (Myth 3/3). Gear cannot be upgraded above Myth 3/3. This change is retroactive for all gear obtained in Season 2. Any Season 2 gear that was created at item level 441, 444, or 447 will now display its upgrade level along the Myth track and can be upgraded at any item upgrade vendor. Upgrading gear along the Myth track requires Flightstones and an Aspect’s Shadowflame Crest for each upgrade. The usual discount rules apply here (if the character has a higher level piece of gear in the same slot, no crest is needed; if any character on the account has a higher level piece of gear in the same slot the Flightstone cost will be halved). Mythic RaidItems from all bosses on Mythic difficulty will be on the Myth track, allowing players to upgrade these items to 447 Item Level using Aspect's Shadowflame Crest. This should make early Mythic bosses much more valuable! This means that the following bosses will now drop items that can be upgraded to 447:
Kazzara: 441 Myth (1/3) Amalgamation: 441 Myth (1/3) Read more on wowhead.com