Been seeing a bunch of speculation whether they do or don't. They seem rather pointless if they do in fact not drop legacy uniques.
For Reliquary Keys, the themes have been legacy, then league-specific and now Vaal themed.
This thread was added on April 14, 2021, with posts from Community_Team.
Original Post
For Reliquary Keys, the themes have been legacy, then league-specific and now Vaal themed.