Seems like more than a rumor, according to the ET link above:
"Dancing With the Stars fans are pretty bummed that dancer Mark Ballas won't be appearing on season 23, but ET has learned that Ballas has clinched an exciting new gig!
A source tells ET that the 30-year-old dancer is actually moving to New York City this month where he'll be living for a year, so that he can appear in a main role on Broadway's hit show Jersey Boys. The musical tells the behind-the-scenes story of Frankie Valli and The Four Seasons, the band responsible for such classics as "Sherry," "Big Girls Don't Cry" and "Walk Like a Man."
Ballas hinted at his new career opportunity in a heartfelt, handwritten letter to his DWTS fans, which he posted on Twitter on Wednesday."
So the question is, will he be Frankie? Guess we'll find out soon! :)