To avoid needing much houserules, I'd include magic as only a minor force. The only magic-users of any sort would be clerics, monks, and sorcerers (and a few related prestige classes). The barbarian, fighter, and rogue would stick around, while the psion, psychic warrior, soulknife, wilder, ardent, lurk, and divine mind would be added from the XPH and CPsi.
Clerics and sorcerers would be rare, with clerics and divine minds getting their power from connections to a few ascended mortals, the only deities of the setting, who would only be able to grant spells/powers to a limited number of mortals.
The XPH races would be used in lieu of the core races, with humans sticking around as the only core race. Most MM critters and races would be left out, with only a few dozen sticking around at most. Illithids, yuan-ti, githyanki, and such would be the main villains of the setting. Gem dragons would of course be the only dragons, aside from wyverns and dragon turtles. Psionic monsters would be almost as common as the more-mundane monsters, while magically-gifted monsters would be rare.
The setting itself would probably be roughly Renaissance-era technologically, but with a largely southeast-asian flavor to the world, with strong emphasis on personal improvement and the search for enlightenment, giving rise to the prevalance of psionics and the decent degree of technological advancement. Republics and socialist nations would likely be the norm, with a few kingdoms, empires, and theocracies managing to stay afloat. The astral and ethereal planes would be rather significantly colonized. Magic would be a distrusted and mysterious force for the most part, outlawed in some regions.