Blizzard has released a massive blog detailing every little aspect of the upcoming new gear upgrade system in Patch 10.1.
Will be available for open world, raid and Mythic+ gear.
Will not work on PvP Gear and very top end items.
Will not work on Crafted Gear.
There are two forms of currencies: Flightstones and Crests. Crests come in 4 different varieties: Whelping’s, Drake’s, Wyrm’s, Aspect’s, each corresponding to an increasing level of difficult content.