If the plotlines were to be about stranded Garlean colonizers, we have Ilsabard. Same for any Allagan ruins reappearing - both Ilsabard and Meracydia. Having them as a narrative point while in Tural defeats the purpose of choosing Tural over Ilsabard and Meracydia (and lessens the point of going to those places in a later expansion, so let's save them or else the cloud cover will never leave).

And while we had VII representation with the Weapons trials in Werlyt, that doesn't mean that we need Garleans involved at all to have a Shinra-esque villain to hit up any references that haven't already been covered- though Aulus and the other Garlean mad scientists have covered everything but the actual super-soldier program of SOLDIER (unless idk you count Nael and Zenos), M'zhet Tia had Nanaki's plotline and BLU for Cosmos Canyon.