Moose, first off, I gotta say I'm a long time lurker and occasional poster and I've always enjoyed your comments, theories and analyses. Basically, anything you write is a good read. As for the topic at hand, to me, it seems like Othard is the logical place for at least one of the other remaining two First Brood. Iirc, there are three major continents on Hydaelyn; Meracydia, Eorzea and Othard. I may be wrong, as I'm not sure if Garlemald counts as a part of Eorzea, or if it's more linked to Othard, or if it's a sub-continent in and of itself, but I do remember a few mentions of "threat continents" with Eorzea being one of the three.
If that's true, then you had 3 dragons in Eorzea (Ratatoskr, Hraesvelgr and Nidhogg) and 2 in Meracydia (Tiamat and Bahamut). The dynamic I read into this is that, when you're basically an immortal being, you want someone who understands you by your side, so it stands to reason the last 2 would stick together. Dragons also seem to enjoy their own space, so with 3 in Eorzea and 2 in Meracydia, it makes sense that the last 2 would strike out on their own. If they went in the direction of Garlemald, chances are they're probably already dead, captured, in hiding, or they've fled. The Garleans aren't the type to just let super-powerful beings live their lives and do their own thing. From what we know of the world, that just leaves Othard.
On another note, I've often wondered about the dynamic between each of the first brood. Obviously Tiamat and Bahamut loved one another, and there clearly was strong affection between Hraesvelgr, Nidhogg and Rataroskr. I'm undecided as to whether R and N were "lovers" in the way that T and B were or if R was more of the "kid sister" to her big brothers H and N.
Incidentally, regarding R and N (don't read this part mucuz!)....
edit: thank you nalien!
I hate the idea that Ratatoskr is gone, but given what happens to Estinien at the end of the MSQ, I wonder if something similar can't occur with Ratatoskr. After all, according to what we've been told, most, if not all current Ishgardians/Coerthans are descended from the people who feasted on R's power. As noted in game, "just a sip" of dragon's blood is enough to awaken the latent dravanian power within them, turning them into a dragon. In a sense, this kinda makes all of these people "children" of Ratatoskr, which, if you look at it from that perspective, adds an extra layer of F'-ed up to what Nidhogg has been doing.
But it also means, if N can be reborn by essentially possessing Estinien, then does that mean R could also be reconstituted somehow? They both essentially had the same thing happen to them, only N's power was concentrated in his two eyes, while R's power is spread across likely thousands of individuals. It's probably a long shot, but I'm kind of giddy at the idea that the true end of the Dragonsong War will come only when the people of Ishgard and Coerthas find a way to "give up" the latent power of R that is in their blood, thus paving the way for R to be reborn.