On Broadway.com's Periscope right now, they have found out there is a new musical announcement expected tomorrow and a hint was that Paul Wontorek had seen it... it was not (among guesses):
Heart of Robin Hood is more of a play with music - the songs do not advance the plot or convey the feelings of the characters - they are more like colour commentary on the side in song form by a band that is separate from the speaking cast.
It may be a coincidence but Mama is closing there early September. With all the baggage the show (Rebecca) has, better not to open it as it will be called a Wildhorn clone in addition to all its legal problems.
Considering that tomorrow is a REALLY bad choice of a day to announce a new show for next season, my guess would be the one show mentioned that has a lead producer with zero Broadway producing experience, Amazing Grace. Here we go again.