User blog comment:Godzillavkk/Star Craft 3 story ideas./@comment-4817-20181224160306/@comment-31277203-20181224170729

It might not have to be just plain conquest. Remember, they never knew what happened to the expedition fleet, so it's possible their return to the sector is (at least initially) just to investigate what happened. However from BW it seemed their focus had been dealing with the zerg. I'm not sure just how much they know on the protoss end.