WHAT WE KNOW:Edit
On September 13, 2006, Universal Pictures announced that director Jonathan Mostow was attached to rewrite and direct Marvel Studios' The Sub-Mariner. Kevin Misher would produce the film through his company, Misher Films, along with Marvel Studios. The screenplay had initially been written by David Self. In 2012, Marvel CCO Joe Quesada thought Namor's film rights had reverted to Marvel, but it was later revealed by Marvel Studios President Kevin Feige in August 2013 that this was not the case, and the rights remained at Universal Pictures.
Since this movie started before the Marvel Cinematic Universe began, there is no telling what Cinematic Universe this movie will fall in.