Dragonriderds of Pern would be a nice non magic setting with a twist...
Fanbased conversion are great and all but unless they are regarding something for which their is a vast amount of freely available info, such as LOTR, then their isn't really enough info available for folks to use as say their would be for those who had the cooperation of the creators or owned the license, nor the resources to produce the eye candy, and pictures that make the books one of those you rarely leave out of reach for long.
Babylon 5 fading from memory may well attribute to the lack of interest where fan conversion go as you say. But why no publisher has picke dup this setting for a D20 sci fi game is beyond me, considering how well developed, detailed, and beautiful it was... i mean Shadows, Vorlons... mimbari, narn.... the drac, corrutive earth gov, the Psi corp..... what more do people want...it's BEGGING for D20 treatment i tell ya BEGGING FOR IT!
when i think of how the games, genre and setting i love could be presented, by some of my favourite games producers... it brings me to tears almost to think of the abject lack of interest most of them show in making the attempt.
I mean i know most want to explore their own avenues, and develop their own things, and don't want to work under the restraints most licenses impose on their creativity and desired direction for the items... but GUYS COME ON!!!! throw us a bone once in a while...

B5, FALLOUT, DUNE.....MARVEL.... We want them! and more..... pretty please!!!!