I think a Regulator faction would really spice things up. I know a lot of people will say that they'd be a dm faction and flame the idea to ashes, but I think with the right ingredients and control it could be a succesful faction.
The members would have to be somewhat deranged to want to "cleanse" the zone - a bit like monolith post-brainwash. The passive would consist (along-side each characters independent story) of collecting intel on the wastelands inhabitants - mingling with them to learn of them - when someone "evil" is discovered, then plans are concocted to purge them - detailed plans as to avoid mistakes (and to extend potential passive rp for even longer, but still keeping it fun).
The hierarchy would also be pretty simple - one Head Regulator (I was thining maybe Sheriff? xD) and the rest being members, with maybe a few "officers". And of course - membership would be invite only.
The aim of the faction would be to purify the wasteland of evil yet to remain anonymous in doing so - remain under the radar for both the safety of the faction and the inhabitants of the wasteland - giving an incredibly passive faction yet still having an exciting, dangerous edge.
It'd pretty much be a more exclusive, righteous, refined version of monolith.
I think it'd work tremendously!