Any new piece of gear that drops at 441 or higher can be upgraded to Item Level 447 on the Patch 10.1.5 PTR using the new ‘Myth’ upgrade track including Mythic Raid, Mythic+ and Very Rare Heroic pieces.
Mythic Raid
In Patch 10.1, Mythic raid items, especially off the first few bosses, have very small value and it seems like Blizzard may be trying to address this.