Demo 8 is the latest demo released in 2017.
The demo features world's 1-7 100% complete with Bowser's Castle being broken. Many levels were remade, most notably Lemmy's Castle, Mario the Pyromaniac, and Gourmet Boo (Now called "Mystery Cabin"). Luigi's World/Mushroom Kingdom has a new level completed and another being worked on. These being Mushroom Kingdom 1 and 2. There is also a boss being worked on in Level 183 in Lunar Magic. It's unclear as to what boss it will be as the graphics for the level are messed up.
This demo is the sequel to the 1-1 Demo.