Crackpot Theory: Thancred will become a Reaper

[Soge01]

1. He lacks the use of his own Aether due to the events of ARR.

Garleans lack the use of their own Aether because of an unknown genetic defect preventing them from doing so. And so, during the days before the invention and mass production of magitek, the Garleans relied on making a pact with Voidsent in order to gain the ability to not only manipulate Aether, but also bolster their own physical strength.

2. The Lemure, the quest givers and one of the very last living Reapers, is based in Ul'dah.

Thancred was previously stationed in Ul'dah by the Circle of Knowing during 1.0 and again by the Scions during ARR.

3. Reapers are the dark assassin equivalents of Rogue and Ninja. And have a long history of using their unique a ability to manipulate void magicks in order to silently infiltrate enemy kingdoms and assassinate their leaders.

Thancred is a highly experienced Rogue, throughly trained in the arts during his academic days in Old Sharlyan and was our main man, besides Riol and the Doman refugees, to go on frequent infiltration missions into enemy territories. One of the most notable ones being the captial of Garlemald before its destruction at the hands of Zenos and Fandaniel.

4. Thancred has experience with possession. He was possessed by Lahabrea during ARR.

Experienced Reapers have extensive experience when it comes to allowing their voidsent called the Avatar, possess them temporarily in order boost their own power even further, though without the Reaper themselves losing control of their mind or body.