What happened to the Itachi Uchiha movie?
This is not a movie. The Itachi Shinden novels are being adapted to a TV release, which will air this spring. I didn't see information about it beginning in March. 

The Naruto twitter account shared a link to TV Tokyo Naruto website which has a small trailer and information about the release, which seems to indicate that it will begin airing in Japan on April 7th.