I've seen or come up with several "alternate" settings for N&S that might fit what you're looking for, though I expect Recon Sourcebook 3 long before I expect another N&S setting book.
Here's some:
Gettin' Medieval:
Setting: Mid to late 1600s or 1700s; Medieval Asia.
Research: Basic medieval-setting movies may be enough for a generic cinematic campaign. (Hero, Crouching Tiger, Seven Samurai or other Kurosawa epics, etc.), though in-depth research will be needed for a more historically-based campaign and is recommended for a cinematic one as well.
Plot: Characters play old skool martial artists fighting for or against the various dynasties of China, Japan, Mongolia, and others. Any MA characters or OCCs from MC are good as is. Other character classes will require some fixes. Gizmoteers are still possible but will require a lower-tech approach, possibly using devices built from springs, gears, water wheels, pulleys, etc.
Skills: Obviously this would require new skill programs and limited skill seselctions.
Tech: Low. No more than basic matchlock or wheel lock firearms. Gadgets will be built using springs and inginuity. Cybernetics will be limited to spring-loaded fantastical creations ala Ash's "robotic" hand in Army of Darkness.
The Age of Science:
Setting: Late 1800s. European powers dominate the globe. Steam and science are king. The old ways are dying out as a new scientific age that promises to solve all human problems dawns. Campaign may be a realistic campaign based on the real world of the 1870s-1900, or may be a fantastical "Steam punk" land out of Verne and Wells books.
Research: Reading old 19th century SciFi or modern Steam Punk genere is good for a general cinematic setting, but historical research is needed for a more historical campaign and is recommended for any campaign.
Plot: Characters play any standard OCC from N&S or MC, though tech will be limited to Steam era. The entire world is your stage with many possibilities: Asia, Europe (prowl the foggy streets of London), America (the western frontier is full of conflict and even a lot of Chinese culture), or Africa.
Skills: Standard with omission or alteration of some of the more high-tech skills.
Tech: late 1800s. In a fantastical "Steam Punk" campaign many of the high-tech may be replaced with "steam" versions, such as steam-driven cybernetics!
Frontier 2000:
Setting: This is the setting of the Big Trouble in Lunar China game I post here. Present day alternate history. Some seemingly minor historical changes in the late 20th century led to a world where permanent colonization of space is a reality by 2000. Permanent space stations and moon bases are in place.
Research: Sci Fi books (obviously) and movies or a study of modern NASA ideas. 2001: A Space Oddesey is a must. Mutants in Orbit can give some ideas for fanciful life in space.
Plot: Standard N&S with a slightly higher tech level and a new theater of operations. Now the many space-faring nations of the world (I used the US, USSR, EU, China, Japan, and India) are in a new colonial race for control of the seemingly limitless resources of space.
Skills: Standard, though new space-based skills may be necessary.
Tech: High. Modern-day with advances in space technology.
I'll post more later...