Threepenny Opera has a great cast, so if the director doesn't mess up everything it should be fine at the very least. And, personally, I'd choose Macbeth.
In that period you can go to see Kenneth Branagh in The Entertainer, Funny Girl at the Savoy, Lady Day with Audra if you haven't seen it on Broadway (same for Alladin, if you like that kind of shows), Motown.
I believe The Play That Goes Wrong is planning on coming to New York next year - but, the Duchess is a pretty intimate theatre with a great box office. But then if the original cast does transfer....
I don't know what will be at the Union, but if it hasn't moved across the street by September, you should consider a visit. In your research, keep an eye out for what will be performing at the Almeida and the Hampstead.