A new article from the Daily Mail states that Jamie Campbell Bower is in final negotiations to portray Gellert Grindelwald in Deathly Hallows.  Remember that does not mean this is confirmed yet!  The article also says,

But Bower won’t shoot his scenes for some time because director David Yates is concentrating on filming as many scenes with Emma Watson, Daniel Radcliffe and Rupert Grint as possible before Ms Watson decamps for university in September.

The trio have done several action sequences, and Daniel and Emma have been working with a choreographer for some big wedding scenes that will be shot in the summer.

Thanks SS!