CaptainStabby said:
Relictors… All day.
These aren't the warp tainted artifacts you're looking for Mr Rogue Trader. Move along now, nothing to see here.
They had crossed my mind (especially as (IIRC) the RT timeline is pre-their excommunication) - but I think I've settled on the idea that the McGuffin is related to The Enslavers - which would tie in very nicely with the Storm Wardens. Plus with our crew and their xeno/archeotech ships the Relictors would want to take all their coolest toys….