The author, Anthony, confirmed via twitter that its a limited edition Dazzler concert shirt. Upon doing a quick google search, I was unsuccessful in finding any additional imagery to affirm its prior existence so I believe it was created for this story. I wouldn't be all too shocked if it was attained from the concert they attended in space, whilst dimension hopping in Style > Substance. Its lovely.
And to the complete shock and awe of precisely NO ONE, the Drag Brunch with Loki was EXCEPTIONAL. Beautiful. Funny. Charming. With a completely unexpected gut punch to my emotions. I would LOVE to see/read/experience further tales from this creative team. Not only did Anthony nail the characters, he managed to further develop and expand upon their world -- their day to day, their community, etc. He introduced charming additions to the MU without feeling forced and without giving the all too common feeling of "I just wanna add my own thing" and without having them steal the focus from the lead characters. The number of continuity nods and pop culture references made was so impressive and appropriate and again didn't feel forced. Teddy's magic sword, The group photo from Gillen's run, their gifted loft from Roberto, the Dazzler shirt, X-Men themed drag show (so appropriate imho), Kate's LA connections (Quire, etc), the relationships fostered during Style>Substance, the Demiurge, etc etc etc It was all just masterfully RICH and entirely satisfying.
Also YAY! And I do believe I see Tommy's hair peeking out the other side there next to Billy.