Cloudier alignment and moral issues
Alignment is out of fashion and has been officially de-emphasized or deleted from newer editions of fantasy games like D&D or Pathfinder, but I do think it can be useful as a character motivation or adventure hook if handled carefully (i.e., not as a stick that the game designer orders DMs to use on players in order to beat them into compliance with the designer’s favorite fantasy archetypes). I wonder what it would look like to make a 5E setting that brought back the old tripartite “Law vs. Chaos” alignment system, and made it a major focus for faction intrigue within that setting.
Inspiration could come from 70’s pulp fiction (especially Moorcock), Babylon 5 (Vorlons vs. Shadows), and the old wargaming conventions that used alignment to determine who could recruit which troop types (IIRC 0E elves and orcs could be Neutral and might find themselves fighting alongside one another, if the price was right). Players could ally with one side or the other, or try to play them off against each other for fun and profit. There would be powerful aligned magic items that might have their own agenda, like the ones in Blackmoor and Greyhawk (Original Recipe™) - not just swords but other weapons too, and spellcaster items like wands, staves, or rings (“Nine for mortal men, doomed to die”


). I never particularly liked D&D’s modrons and slaadi anyway, so if I were homebrewing this I would use Pathfinder’s axiomites, inevitables, and proteans, but obviously the Coastal Wizards and 5E 3PPs could not use Paizo IP that way.
Would it end up just being Lawful Neutral vs. Chaotic Neutral, or is there another way to make an interesting dichotomy? Gen X kids like me learned D&D from the red Basic sets, and even back then TSR had already muddied the waters somewhat (IMO) by explaining Law and Chaos as just Good and Evil with a different coat of paint. In my old gaming group, we struggled to understand the more arcane AD&D alignments like True Neutral, and in general alignment issues rarely came up much at the table. We played lots of the classic B/X and 1E dungeon crawl modules, and alignment never seemed particularly relevant to most of them. We frowned on what would now be called “murderhobo” behavior as a distraction from mission objectives and a waste of everybody’s valuable table time, so DMs did not really need alignment to make players behave.
It might be tough to get newer and/or younger 5E players interested in this rather esoteric style of play, but I think some OSR games are already using three-way alignment. Mystara might be a good fit for this idea since it was the original setting for B/X and BECMI.
EDIT: 0E did not use the Known World / Mystara.