While I do plan to (eventually) make a base Save, where the extra "kingdoms" are will probably depend on the story I decide to tell for the given save. If I don't care about royalty in that save, I probably won't do anything beyond the default of Ondarion. But if I set up something beyond that, there are some good candidates, most of which have been covered...
Windenberg is obvious. I even built a Von Windenberg Castle based on Highclaire Castle (aka Downton Abbey) when the Castle Kit came out. Available on the Gallery (plug, plug)
Henford on Bagley just feels like a smaller part of a larger nation (with Britechester), so that may only get a Dutchy if anything. This will probably vary by save, too. Britechester, by contrast, won't get its own nobility... even if there was room for it.
Tartosa will likely become a Principality, like Monaco. I don't play there often, so setting up (and cheating up) a royal household there and then letting things go feels about on brand for me.
Tomarang may well get some sort of Nobility. I need to do more research into South East Asian historical kingdoms first
Innisgreen seems easy, but as they have the fairy and non-fairy sections, maybe it will be under contest between the humans and the Fae... heck, that may even be where I put my spellcaster Nobles. This may also be a by save thing.
Forgotten Hollow - Vlad will finally have a day (night?) job in my saves, as Vampire King... or maybe Prince (VtM, anyone?)
Glimmerbrook - probably not. Not because it's small, but because I see it as "ruled" by the Sages as a council of 3.
Ravenwood feels like it should have a creepy old haunted castle around somewhere, but that will probably end up being a by save thing.
Nordhaven, Mt Komorebi, and Ciudad Enamorada (which I really need to play in more) could get something, but don't "feel" right to me, kinda like Britechester.
The "US/American" worlds of Willow Creek, Oasis Springs, Chestnut Ridge, Del Sol Valley, San Myshuno, Brindleton Bay, Evergreen Harbor, San Sequoia, Copperdale, Moonwood Mill, and Gibbi Point* likely won't get any Nobility unless I make some drastic changes. I don't care what Judith Ward or the Landgraabs think.
And anything can happen in Newcrest.
*I know Gibbi Point isn't neccisarily American, and yet it has this weird feel of a mix between somewhere betwen rural Puget Sound, Yellowstone, and New Zealand, so I can't picture a monarch there either.