The illusion trick was never usable to get into the Emperor's room, his room is not physically connected to the rest of Ssra. You click a portal and it teleports you.
I don't know if it's the case any longer, but in days old those four small rooms off of the Emperor's main chamber did not have the CotH restrictions that the main room did. So if you know how to get past the red electric "walls"/doors that separate those little rooms from the main room, you can get a mage up there, summon a whole raid, and bypass keying that way.