Namor would work if they cast the right actor. The Rock was fairly convincing in his heel persona. And he can put @$$e$ in seats. As a second tier character they would need someone with some star power to attract the right attention (see Fox casting of the new FF on the WRONG way to do that). People hate on the Ghostrider movies, often with legitimate arguments. As a fan of the character I was very happy to see him get two movies, even if they weren't perfect, or even close. Point is, those films likely never would have been made without Cage's involvment. I would much rather see a Defenders movie featuring Namor, Hulk, Dr. Strange, Silver Surfer and Valkyrie (Beth Phoenix?) than a Heroes for Hire show called the Defenders.