Evidence that Allagans had presence outside the Source?

[Torquil]

From the lore book entry on the Hyperstellar Downconverter (pg 167):

...was developed to communicate with Dalamud...It was later repurposed and improved upon to facilitate communication over the massive distances between stars.

Now it's possible this was just a fun toy technology and they had no idea if it even worked. However, it seems plausible that the need for and practical testing of such a technology means the Allagan had a presence on a world other than our own. (or, to be a party pooper this could have just been used by Xande to communicate with The Cloud of Darkness).

[Enkidoh]

We know the Allag had interstellar travel, the Ragnarok internment hulks were clearly stated repeatedly as being starships, so some kind of interstellar communication system goes hand in hand with that. Of course that then leads us to the interesting possibility that remnants of the Allag may indeed still exist as colonies on other planets.... but I don't think even SE really takes that idea that seriously, given Hydaelyn is the game's focus and always will be. But it's still an intriguing concept to think about regardless...

[PArcher]

Well, we have the capability for interstellar communication (somewhat) and space travel, yet we're still Earth-bound...

[Hinoto-no-Ryuji]

Outside the Source, where "Source" refers to our home dimension in relation to the other Shards? Or outside the Source, where "Source" refers to our planet only?

The tricky thing is, the term "star" would appear to be pretty catch-all in the game, referring to the pieces of constellations and other visible astral phenomena (Dragon Star, etc), as well as "planet" and possibly even "reality" (see: the theory kicking around that Midgardsormr's "came from another star" claim means that he's from one of the Shards). This makes it hard to parse what exactly "interstellar" means in the context of the Allagans. I don't think it refers to the Shards in this case, though, if only because communication with them doesn't seem to be so difficult as to require fancy new technology (the significantly less-advanced Mhachi civilization managed it, after all, unless that was thanks to Xande's tech weakening some sort of barrier). The mention of Dalamud, an object that definitely existed within our own reality, implies a physical distance as well.

Which brings us back to the question of what exactly the Hyperstellar Downconverter was refined to communicate with. It being a device for inter-dimensional communication comes with a built-in answer, but an intra-dimensional one? I'd think an actual colony established during Allagan reign would be something pretty major that would have come up in our various dealings with and explorations of Allagan history and artifacts by now, but maybe there was Allagan starship floating around out there that eventually settled somewhere. Or maybe there's an Allagan Moon Base! We may have dealt with a whole hoard of things from Allagan antiquity, but we've never dealt with a contemporary population of them that has survived up to the modern day, isolated in a galapogos-esque environment and culture. That could be cool. It would almost certainly fall short of expectations - it's hard to extrapolate how a singular, isolated culture might evolve over five millenia - but it's a potential Neat Thing that could be explored when/if we run out of planet.