I don't see the point in Thancred remaining a normal Gunbreaker. The fact he has a major weakness in that he can't use his own aether to charge his gunblade cartridges and is forced to rely on the Scions or anybody else for that matter to do it for him should really be treated as a last resort instead of a natural constant
We have Cid's Ironworks, the remnants of the Garlean Empire and the people of Sharlyan, any of whom could figure out an alternative method for Thancred to charge his gunblade cartridges.