More world please. The basic reason why I made this was so that we could see how much more of Militiregnum there was.
I don't see why we should assume any of these. All we need is to just place the new lands far away from the known lands to justify for their not being discovered. Nexus Force wouldn't have told Miltians anything for two reasons: 1. They have a policy of not affecting planets' natural evolution (in things like technological advancements, scientific discoveries and exploration of the world) when they can. At least, I think I said so once somewhere, I think it was the Fall of the Baron, 2. The Nexus Force isn't really there. The few Nexus-Forcers that have made it to Milt would have scarcely the time or mind to check the planet's geography (Talmid, Thingguy, Luke, Seton, Legoboy, Sharpie, the Gemini, Shard, Blaze, Muffin, Axe and Major are I think the only known members to have arrived and they did so in a rush). Same goes for thedude and his army. While from some point on, he could explore the world further, his focus hasn't really been on it and that is why only Karribea has been discovered so far. While there's a lot of advanced tech around, most of it would go to the Rhoddwr Marwolaeth, the PCG Dimension or stay grounded. In the end the Red Mythrans are the only possible people who might have seen what others haven't and have the ability to land on Milt. But I'd hardly describe them as descriptive and eloquent enough for the job of geographers.
All in all, what this means is that our complete lack of what's out there is justifiable (at least until we get contact with the NF). There could be anything out there and we don't need to worry about why they didn't know.
I like the idea of something tropical, though we do have Elepharia, which turns out to be bigger than I thought. But I wouldn't rule anything out yet, I'd like to keep our possibilities open. Perhaps, try to incorporate more civilisations from our race palette like Indians and/or American Indians.
As far as the Elves go, I thought they might have actually migrated through the Rift, but it is one possibility to explore that they may have their small island somewhere.
There's nothing official said about Book 4 (excepting N_B's expression of desire to write that book... in times past). As far as unofficial, there's the Incorrect Trailer I made and a mental note to myself saying: "STOP TRYING TO CONTROL EVERY BOOK!"