Feldstein was a member of Workshop Theater Company at 312 West 36th Street in Manhattan and developed some of his scripts and musicals there. "Une Parisienne in New York", one of his latest work with 14 songs in English and French by songwriter Greta Gertler, is one of these projects. "Une Parisienne in New York" was presented at Dixon Place in February 2018. Another is "The Kingdom of Vincent Grapelli" with singer/songwriter Rivky Grossman. In March 2015, his play "Happy Chrismukkah", about a stressed out New York couple dreaming of escaping to Australia, was a winner in the NYC Playwrights "Save the Rom-Com" competition. A workshop of Your Youtuber a monologue written by Feldstein and performed by Ty Baumann was presented in May 2016 for the Flying Solo Theater Festival at the Secret Theater, LIC, New York. Subsequently, Your Youtuber won the Elite Theatre Company 8th Annual One Act Play Competition. And was mounted in January 2017 in California. Also in January 2017, at Workshop Theater, "The Man Who Made New York" a full-length play by Feldstein about Robert Moses, NYC's master-builder, was first presented. The play was directed by Robert Kalfin.