sng said: "So if they were to bring in someone to write a song or two for Act 2, who could it possibly be? JRB?JeanineTesori?"
Jeanine Tesori, I would personally find the best fit, but from afar I'm getting the impression that the creative team would be extremely uncomfortable putting someone else's music in a Sondheim show.
It's a shame because musicals are a team sport, and making the second half as polished as possible, would honor Sondheim's contributions, because if the second half is as good as the first, it will be performed more often.
Watching it last night, I found the first half at times stunning. It was way better than Sondheim's Bounce/ Road Show which I caught in Chicago. The second half was respectable but certainly not good or memorable. The conceit of why people stop singing made a level of sense, but at the same time, people go to a musical expecting to hear songs.