According to Spanish site www.elmulticine.com Emily Blunt has been in talks to appear in Batman v Superman: Dawn of Justice. She was rumored to have turned down the role of Black Widow in Iron Man 2 but has recently appeared in Sci-Fi films such as:

• Edge of Tomorrow
• Looper

Batman News followed up with an article declaring this rumor a hoax.

Source

• www.elmulticine.com/noticias2.php?orden=454890
• screencrush.com/the-wrap-up-emily-blunt-edge-of-tomorrow-poster