Mythic+ testing in Beta came up with some interesting results to the reward system of Mythic+ as it follows:

          Weekly chest has a chance to bring you additional items:

•  From 1 to 3 Pieces of gear;
• A Mythic Keystone, at a appropriate Keystone level
• Artifact Power for your Heart of Azeroth.

Also, there is a chance that the items dropped into the chest to Titanforge as well, excepting Weapons and Azerite Armor.

           Azerite Armor Weekly Chest breakpoints

Azerite Armor can’t be farmed from end-of-dungeon drops. Players are only able to receive Azerite drops only from their Weekly Chests, it seems. As players noticed, Azerite Armor’s item level gets increased by hitting certain breakpoints, rather than increasing every other Keystone level.