Interesting Question Regarding Voidsent.....

[Theodric]

What is the source for this? Which cutscene/dialogue specifically, because I do not recall ever coming across this plan regarding the Thirteenth.

There isn't anything to pin down other than head canon. To the point where it seems to have left other posters across a number of different FFXIV lore discussion venues scratching their heads:



In other words, there isn't any real solid evidence to speak of and any attempts to claim otherwise will very likely fall prey to bias and attempts at filling in gaps with a particular narrative.

Sorry to not be of more help!