That would be too FFV/FFIX/FFXI like, so it's a bad idea sadly since XIV isn't allowed to nod to previous games in the series.

Serious note though, it would be pretty interesting if it happens since FFIX and FFV did it pretty well, especially when the worlds merged (FFV) so they have quite a bit of breathing room. XI did it well with Abyssea because that storyline is while their vana'diel resembled ours it was clearly a different dimension, one where we died at the end of CoP and Al`taieu never slipped out of "present" reality and still on the moon.

There's a ton of possibility with the "parallel world" approach and SE has proven they could make it flow within a timeline and still be coherent quite well.