Hmm, I don't get why you think certain campaign settings wouldn't translate well. 4e is still old fashioned D&D, it just has streamlined rules that make it easier to run and play (at least, that's what the designers are aiming for).
The two setting that you mentioned are actually two of the settings that I think would MOST benefit from 4e. If magic items cease to be such a powerful balancing force then Midnight can do away with the annoying Heroic Paths that never quite worked for me and stick to the sheer awesomeness of the setting itself. Likewise, Conan used magic very, very rarely (Phoenix on the Sword being one of the notable exceptions, where he's temporarily given the use of a magic sword to defeat a Gorilla Demon). Both setting would thrive on the "damn the torpedoes, full speed ahead!" approach. Hell, Howard practically invented that approach.