If so... meh?
"D&D Guildmasters" might refer to the Dungeon Master's Guild, and the setting being opened up for use there by fans with this initial book providing the introductory framework.
Ravnica might not be the only setting that will be officially announced this year so there's still hope for Planescape, Eberron, Spelljammer, etc.
Didn't they say there were two settings they hadn't announced yet for this year?