What do you think they gonna add? There is some addon (ALL THE THINGS) showing 900ilvl loot from the old classic green drakes, so they might be up for the duration. I havn't found anything about that so far, but I think it's some datamined stuff.
I basically think, there will be a new "timeevent"-raid, i.e. these 4 drakes or maybe BWL/AQ40/AQ20, since silithus is pretty related to the current lore.