For Solution 9, I'm leaning hard on them being a civilization from another shard that managed to teleport their way there during the last calamity (they're originally from the shard that was re-joined but were advanced enough to keep the core of their civilization intact during the process). They've then kept a low profile for the last number of years as they've been in the process of figuring out just what their new home looks like.

They're far too advanced looking for the source to have been there a longer amount than a couple of years as their tech would definitely have attracted the Ascians or Garlemalds attention before now. It's not impossible to rule them out being a shoot off of the Allagan Empire at some point but given their level of tech too much time would have passed for them to not have significant influence on the planet at that point. Even Garlemald at it's height had projected power and influence over half the world.

It's still all hypothesis right now but a civilization from a fallen shard that managed to survive a re-joining would be a big deal expecially for Y'shtola as she would be all over that in her side quest to develop intershard transport.