Revamping Gamma World for 5e and beyond.

 Revamping Gamma World (for any edition) is a massive undertaking, given how much technology has changed in just 40+ years.  The internet was not available to most, biological science has changed in leaps and bounds, and locales (such as Pittsburgh / Pitz Burke) have changed as well.  

GW as a system would probably be best as a modular toolkit - want your mutations to be less gonzo? Don't add the mutations (the majority of which are really psionics anyway).  Don't like the idea of nuclear war being the source of the Disaster?  Make it nanotech/grey goo or bioengineering gone wild.  Want to put it on an extrasolar planet colony gone wrong from native viruses?  Consider the fact that the setting is a primitive setting a couple hundred years after the Disaster, *nobody* is truly going to know the true origins of the Mess they're living in.  

Personally, I want a less gonzo game, less character death, an emphasis on purely physical mutations with psionics/powered mutations being rare (close to how AD&D treated psionics), more Cryptic Alliances that characters can join, and more mindless creatures (without powers) for a more hack-n-slash feel on occasion.  Many of the Monsters are sentient and should be available as character genotypes.  

For the monsters, not all of them should have access to the psionic powers, reserving them to the 'elites' of each species. Want to nuke your hometown to make it a setting? We need a homebrew toolkit to guide GMs on successful setting creation (for example don't put Red Death next to more tolerant Alliances, for there's a pretty good chance they'd wipe them out) Artificial Intelligence and other robotic life forms could be an entire booklet worth of rules and options.  

In fact, the format of Gamma World publications should be more along the lines of the Complete Classes books of AD&D - softcover (better covers though), smaller page counts, lower price points, with foci being on Mutants, Plants, Animals, Monsters, Androids, Technology, etc. An entire book could be devoted just the Origins for the Disaster!  

There are so many variations of the post apocalyptic genre in lit and media, and Gamma World should embrace all of them.  The only way to do that well is to make *everything* optional (i.e. modular) with more styles of campaign settings (some of which I suggested above). This ensures that Gamma World wouldn't be immediately outdated the moment it's published, which is partially the reason why there have been so many versions.

2¢