Shadowlands Patch 9.1 will bring new Optional Reagents to upgrade your Legendaries and a few new fun recipes.
Upgrading your Legendary
There are two new ranks for Legendary items: Rank 5 (iLevel 249) and Rank 6 (iLevel 262). There is no new recipe for the new rank of base items, instead you can use the new optional reagent 
Vestige of Origins, which increases the item level of the attached legendary base armor piece by the equivalent of 2 ranks. So, basically, you can add it to a Rank 3 to get a Rank 5, or a Rank 4 to get a rank 6.
Vestige of Origins can be crafted by Blacksmiths, Jewelcrafters, Leatherworkers, or Tailors. The 
Tome of Origins recipe is a reward from the 
Untangling the Sigil quest in chapter 4 of the new patch 9.1 Chains of Domination quest chain. (chapter 4 requires Renown 44)
To upgrade the legendaries to these new ranks, you will also need 
Soul Cinders from the new 9-12 Torghast Layers.
New Crafter's Marks
Players with Alchemy, Blacksmithing, Engineering, Jewelcrafting, Leatherworking, and Tailoring profession can craft two new Crafter's Mark recipes. (They didn't add new ones for Enchanting)
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Crafter's Mark III sets the item level to 200 and the required Level to 60. 
Recipe: Crafter's Mark III is sold by Duchess Mynx. Requires an Honored reputation with Death's Advance, and it costs 2000x Stygia. -
Crafter's Mark of the Chained Isle sets the item level to 230, but it adds "Unique Equipped: Shadowlands" to the crafted item, so you can only wear one item upgraded with it. 
Recipe: Crafter's Mark of the Chained Isle is sold by Archivist Roh-Suir. It requires Tier 4 research level with The Archivists' Codex faction and it costs 2500x 
Cataloged Research.
Cataclysm Timewalking vendor
Kiatke, the Cataclysm Timewalking vendor, now sells classic recipes that were removed in Cataclysm:
Recipe: Greater Arcane Protection Potion - Alchemy
Recipe: Lean Venison - Cooking- Recipe: Big Bear Steak - Cooking
- Recipe: Lean Wolf Steak - Cooking
- Schematic: Ice Deflector - Engineering
Pattern: Robe of Winter Night - Tailoring- Pattern: Stormshroud Shoulders - Leatherworking
- Pattern: Stormshroud Gloves - Leatherworking
- Pattern: Stormshroud Armor - Leatherworking
Alchemy
- 5 new recipes to create colored powders that you can throw on other players:
Blossom Burst, 
Glory Burst, 
Marrow Burst, 
Torch Burst, 
Widow Burst. All 5 recipes can be looted from Invasive Mawshrooms in Korthia. (rare drop, not 100%) 
Stones to Ore transmutes 4x 
Porous Stone and 2x 
Shaded Stone into a bag of Shadowlands Ores. The recipe is sold by Archivist Roh-Suir. It requires Tier 4 research level with The Archivists' Codex faction and it costs 2000x Cataloged Research.
Enchanting
Enchanters can create a new pet leash: 
Anima-ted Leash. The recipe is sold by Keeper Ta'hult in Oribos for 15x Polished Pet Charms.
Inscription
New vantus rune: 
Vantus Rune: Sanctum of Domination. The recipe is a random drop from bosses in the new Sanctum of Domination raid.
Jewelcrafting
Porous Stone Statue and 
Shaded Stone Statue are two new stone objects that you can place on the ground where they will heal you for a short time before they disappear. (2 Min Cooldown)
Design: Porous Stone Statue is a rare drop from Relic Cache container. These can spawn randomly in Korthia.- Design: Shaded Stone Statue is a rare drop Riftbound Cache container. These can spawn randomly in Korthia.
Leatherworking
Elusive Pet Treat - Drop a tiny bone wielding golem for your companion pet to chase around for 30 sec. (10 Min Cooldown) The recipe is a reward from Korthia World Quests.
Pallid Bone Flute - Play a haunting melody, inspiring those around you to dance. (10 Min Cooldown) The recipe is a rare find from Pile of Bones in Korthia.
Pallid Oracle Bones - Use: Consult the bones to learn your future. (15 Min Cooldown) The recipe can drop in De Other Side from the Challenger's Cache.
Tailoring
Shrouded Hand Towel is a random drop from Humanoid mobs in Shadowlands.