The most basic decisions in creating a D&D character are the selection of race and class. To these parameters I would propose adding a third dimension, culture. The purpose of the cultural parameter is to sort through a large array of chargen options to create patterns in the campaign world. Examples:
Culture one (bog standard fantasy)
races: human, half-elf, hill dwarf, high elf, halfing, gnome
classes: fighter, cleric, wizard, rogue
prestige classes: arcane archer, eldritch knight
Culture two (the vaguely Norman guys invading the island home of culture one)
races: human, half-elf, grey elf, mountain dwarf, gnome, half-orc, orc
classes: warmain, paladin, cloistered cleric, magister, unfettered, mageblade
prestige classes: assassin, tactical soldier, archmage
weapons: bastard sword
Culture three (Celtic? Norse? Whatever.)
races: human, half-elf, wood elf, deep dwarf, troll
classes: barbarian, ranger, spirit shaman, scout
Culture four (Orientalist adventures, ahoy!)
races: human, mountain dwarf, wood elf, goblin, hobgoblin
classes: samurai, shujenka, sohei, wu jen, ninja, monk
prestige classes: contemplative, ronin, dragon samurai, kensai, ghost-faced killa
Members of each culture would speak a cultural tongue in addition to Common. Characters would only have access to classes, prestige classes, feats, etc. from their own culture. To add something from another culture I envision some kind of mechanic hurdle has to be jumped. Maybe a feat 'Worldly', with a pre-req of speaking one or two other cultural languages.
I would also make some classes non-culture specific. I'm thinking here about the NPC classes, the Generic classes from Unearthed Arcana, and maybe self-taught classes like Sorcerer. World-spanning organizations might have prestige classes outside the culture system as well.
An additional benefit is that a clever DM can filter out particularly annoying class/race/whatever combos. Hate spiked chain fighters? Put spiked chain in one culture and the fighter class in another. Make the players work to achieve the most tasty cheese.