User blog comment:KarebCree/Thorian -- a possible 'first' Reaper race?/@comment-4950455-20120629040722

I never thought there was an in-game connection of any sort between the Thorian and the Reapers, so I wasn't surprised by the EC shooting this down.

Out of game, though, it wouldn't have surprised me if they were meant as thematic 'opposite numbers', with the Thorian being the organic equivalent to the Reapers' "pinnacle of synthetic life".