I think it's pretty cool, but not unexpected.  Namor was extremely popular in the Golden Age, with more stories seeing print than both Human Torch and Captain America.  Plus he was in print before almost all of those characters you listed.  Then, as now, he was unique among the 'typical superheroes.'  Clearly Clint Eastwood has an affinity for the anti-hero, and Namor was the first the anti-hero of Marvel Comics.
 
I remember reading somewhere that Jack Lemmon was a big Sub-Mariner fan, as well as Nick Cage.

"I think it's pretty cool, but not unexpected.  Namor was extremely popular in the Golden Age, with more stories seeing print than both Human Torch and Captain America.  Plus he was in print before almost all of those characters you listed.  Then, as now, he was unique among the 'typical superheroes.'  Clearly Clint Eastwood has an affinity for the anti-hero, and Namor was the first the anti-hero of Marvel Comics.  I remember reading somewhere that Jack Lemmon was a big Sub-Mariner fan, as well as Nick Cage. "

I think Babs may have found her soul mate...

" @Rheged: Hey, maybe I am underestimating his popularity.  My opinion is based on his lower sales numbers during the Golden Age compared to the other characters I mentioned.  And considering those other characters went on to become household names, I'm glad the Sub-Mariner is the one who stood out and was best-liked by someone whom became as high-profile as Clint Eastwood.    As a matter of fact my father's favorite super-hero as a kid was the Sub-Mariner as well.  I remember him telling that after correcting me on the pronunciation  of his name (I was saying "Sub-Mareener").  My father was born less than two years after Eastwood making them both part of the generation that fought the Korean War.  I have/had five uncles that served in WW II and another whom served (along with my father) in Korea.  When I was a kid,  I asked most of these men who their favorite comic character was when they were a kid.  Besides the time Dad told me about the Sub-Mariner, the only super-heroes mentioned were Superman and Captain Marvel.  Some of my uncles prefered Flash Gordon, Tarzan, the Lone Ranger or the Green Hornet (the last two of whom my Dad remembered fondly from their radio shows).    I just want to say I'm not trying to sell Namor short.  Not by a long shot. "