Billy’s signature Martin
It's out. The only difference from a hd28 is a shorter scale, 1/32 more narrow nut, and the sticker on the inside which isn't even signed. All for $400 more than a hd28.
https://www.themusiczoo.com/products/martin-billy-strings-d-28-signature-guitar-natural
They will probably sell a lot of the X series though.
https://www.themusiczoo.com/products/martin-d-x2e-billy-strings-signature-acoustic-electric-natural