A few weeks ago, I mentioned an idea I'd had based upon a stone age setting. I've turned it over some in my mind, and here's a quick idea for how I'd run it.
Take the Legend of the 5 Rings rules. I'm mostly familiar with first edition, so the lack of samurai kata and stuff makes some sense, plus a simple split between warrior and magic user makes things much easier.
The five elemental attributes still fit nicely, though I might rename Void to Spirit.
Skills would function the same, but not broken down by 'unclean' skills. A warrior would work with any animal he hunts, a shaman would speak to the different spirits, know herbalism and poisons (probably), and so forth.
The different spells would still be usable. Making weapons out of elements is easy enough, causing various elemental motions is easy too. And of course, the basics of sensing, communing and summoning elements works fine.
I'd have to modify some damage from weapons I'm sure. I could easily make a stone axe a 3k2 weapon, which is made especially deadly since I don't think there's much in the way of armour to be had. Plenty of other weapons would be usable too, but at a _k1 level.
Seems pretty straight forward. I'll have a go at how it converts to D&D at some point too.