User blog comment:Vivaporius/Extra-Galactic Invasion Campaign Idea/@comment-3398633-20120707204610/@comment-10514705-20120707235538

Yes, for if it wasn't an AT it would be breaking Canon to go to have a gate created by the Old Ones to another galaxy. Since the Old Ones modifying races is one thing (actively stated in the fluff they modded several) whereas constructing this gate and deciding the fate of the Old Ones conflicts with the Canon in the similar vein that someone deciding that the Blood Ravens are in fact the successors of the Thousand Sons conflicts it.