You need some legends or icons added to that list to make it exciting. The problem with a Broadway con, is that unlike a Comicon, fans can look at that list of guests and say "yeah, I can or have met all of them at a stage door. Why would I pay?" You need Chita, Liza, Bernadette, Patti, Channing.
You need rare performers. Broadways fans have a lot of access to stage actors. The TV and movie people at other cons we have no access to.
"The sexual energy between the mother and son really concerns me!"-random woman behind me at Next to Normal
"I want to meet him after and bang him!"-random woman who exposed her breasts at Rock of Ages, referring to James Carpinello