As you might guess I have no problem with one class covering multiple social positions, and social positions covering multiple classes.
Agreed. I'd look at feat chains or themes as a way to differentiate the different social classes:
For faux Japan:
Samurai have feat chains for warlord-ish 'manage your troops' training, and chains for sword schools, in the style of the weapon mastery styles in Dragon 368. Something for the iconic Nito Ryu is necessary:
Nito Ryu Student (Multiclass)
Prereqs: Dex 13, any martial class
Off-hand weapons you wield gain the defensive property. You gain (some unspecified feat power).
Nito Ryu Adept
Prereqs: Level 4, Nito Ryu Student
When you wield a defensive weapon, the AC bonus it confers is equal to your Dex bonus. You can swap a level 3 or higher power for (another feat power).
etc.
Kensei is probably a paragon path about building a relationship with your weapon.
For priests:
Feat chains for the priestly traditions (Buddhism, Shinto, Onmyōdō) all have Religion skill training as a prereq.
Buddhist powers are divine in nature and tend to be about pacifying outsiders or healing allies.
Shinto powers are primal in nature and tend to be elementalist in theme. Summoning allied spirits is a big deal here.
Onmyoji powers are arcane in nature and tend to be about creating zones and controlling movement.
For monkish people:
Warrior monks - yamabushi and sohei - maybe have iconic weapons training. I'd like to see sohei as psionic characters with feats to make Radiant attacks with polearms, and yamabushi as wardens sounds great.
I suppose if you're a contemplative monk and you get in a fight, the monk and psion classes are fine. Artificer might be cool to use here too.
Witchy people:
Mahoutsukai as locks (with reskinning and a focus on demons and blood magic) and shugenja as a whole range of elementalish magicians (dragon sorcs reskinned as fire priests?) sounds great to me.
Sneaky people:
Rogues and assassins are great! Wooo! Rangers too, I think. And really especially mystical ninjas could be locks, avengers, etc.
For faux China:
Fighty people:
Warlords are important here! Fighters cover the rank-and-file military. Lone warriors - the wuxia - are most likely monks or battleminds, since they are often depicted with nigh-magical powers like qigong flying and sword projection and stuff. Swordmages too!
The fightly primal classes are great for nanban (southern barbarians) and warlords and archery rangers are good Mongols.
Sneaky People:
Lin gui (forest ghosts) are probably rogues, rangers, and all the stuff that ninjas are in Fauxpan.
Priestly Magicy People:
See above for Buddhists. Taoists work like Onmyoji, and Confucianists are probably wizards with an emphasis on compulsions. Wuren are elementalists again, so might as well use the shugenja stuff for them.
Crazy mystics-of-the-mountains are wardens or druids? There is a strong tradition (see Journey to the West) of animals learning magical transformation abilities via meditation and study of the Scriptures.