Parmandur
Book-Friend, he/him
Ah, yes, that is what I thought was meant by your post.No, it was not something for AL. It was a design workshop that the attendees had to sign up for. You may be remembering the Open that Garrett mentioned.
Still don't think Undermountain is in the current offering, since they have emphasized Planar things so much and haven't said boo recently about Undermountain or Waterdeep (Mearls just recently directed somebody to the DMs Guild for old Undermountain stuff if they wanted to explore under the Yawning Portal). I am also fairly certain we will only see one AP book, which will likely be set in Lantan, before going cosmic. They have given every indication of working on only one book of adventure material moving forward.