So I've heard this discussion quite a bit on the Lego Messageboards, being an avid member myself, and it's got me thinking- Alongside Chima, should we just go ahead and call Knighton one of the Sixteen Realms?
Aside from the fact that it's insistently referred to as a realm (which could, of course, just be medieval terminology), we've seen several connections between Chima and Knighton. For example, in episode 3, the Fortrex has the Chi Temple and Eris programmed into its database as holograms for the training area. One could argue that it's nothing more than a cameo/easter egg, but it does make you think. Anyhow, if Knighton IS confirmed to be connected with Chima, then that would make it one of the Sixteen Realms.
Also, on a lesser note, should the Clutch Powers world be considered a separate realm? We know he exists, and clearly, his world has largely different 'rules' as Fenwick called them, from Ninjago's- Namely, creation sparks, the presence of lego bricks being used in just about everything, even functioning space ships, and people being referred to as minifigures who can, likewise, take themselves apart without any harm whatsoever.