NOTE: This is not a list of features that aren't implemented, this is a list of upcoming features. Details here are not final, and are subject to change, or may be largely speculation.
The original Saber Slimes were primal slimes that are now long-extinct, however their lineage lives on in the feral largos inhabiting the Wilds. These slimes would like nothing more than to make you their lunch! They're coming with the Ogden's Wild Update (1.1.0).
Nothing much is known about Quicksilver Slimes. Not even the 7Zee Corporation and the rest of the world know about their existence. But we do know one thing about those slimes, and it's that they live in the Nimble Valley owned by Mochi Miles. They will come with Mochi's Megabucks Update (1.2.0).
The scrapped Meteor Slimes might still be added in a future update, but this is still uncertain.
The kookadoba fruit can be only found within the Wilds. You will be able to bring them to Ogden in exchange for unique rewards. (1.1.0)
More Zone Sections/Sub Areas
Current zones will get more sections added to them and there will be more sub areas for you to explore in the future.
More Treasure Pods
More treasure pods are planned to be added in the future updates.
Adorable Drones will be added, allowing you to automate parts of your ranching experience. Manual ranching will be still required, but drones will reduce your workload and leave you more time to explore. They will be added with Mochi's Megabucks Update (1.2.0).
This mysterious gadget might be added in a future version, since it's referenced in the code. It has a good chance to be a defense against tarr.
Iron Rancher Mode
This mode adds a replayable survival-like experience to the game. It has you race against time to collect quotas of various plorts across multi-day rounds. Each round will also include mixed rules and various challenges, including vampiric chickens, random plorts, random tarr spawns, increased hunger and more. This will be added with Viktor's Experimental Update (1.3.0).
This mode will be much more relaxing compared to Adventure Mode, where the Tarrs don't exist! This will be in Ogden's Wild Update (1.1.0).
5-Day Rush 2.0
The 5-Day Rush will be revisited and improved with Mochi's Megabucks Update (1.2.0)
Ogden, Viktor and Mochi will offer you a daily mission as work-for-hire in new mini zones across the world. These missions will offer unique rewards as you earn favors for each rancher.
Ogden will ask you to collect the rare Kookadoba Fruit that only grows in the Wilds. (1.1.0)
Mochi will ask you to herd the Quicksilver Slimes to corner the market with their plorts. (1.2.0)
Viktor will ask you to perform experiments in a virtual environment. (1.3.0)
It is unconfirmed whether BOb will receive a new zone.