I've been mulling for the last month or so an uncommonly used scenario - what if the "Aryan Invasion" which seems to have sparked the end of the Indus Valley Civilization instead pointed northward, invading China via the Gansu Corridor?
This isn't as bizarre as it sounds. At that time (1,700 to 1,300 BC or so), Indo-European pastoral groups probably comprised the dominant, if not the only, ethnic group in Central Asia. And we know there are Caucasian mummies in the Tarim Basin from this time period, probably the ancestors of the Indo-European Tocharian peoples known from around 1,500 - 2,000 years later.
At around the time of the Indus Valley Civilization, China was in the middle of the Shang Dynasty, and still roughly confined to the Yellow River Valley. Clearly unlike the IVC, the Shang were not in decline due to climactic or other mysterious reasons. That said they had a roughly 600 year history, so some POD could undoubtedly be found. If Hendryk or someone else could point me to some good sources I'd be obliged.
Regardless, if a POD occurs which allows for the occupation of the Shang, it could be pretty much it for the Chinese language and culture as we know it, as it was restricted to a comparably small area at that time.
The resulting hybrid culture would be Indo-Aryan speaking, but probably still overwhelmingly racially Asian. Although admixture between North India and Western Eurasia has been proven to be pretty high, it seems the bulk of the migration happened earlier than the Aryan migration - perhaps when Dravidian-speaking farmers migrated in from Iran. So you'd end up with a China where people are marginally more Caucasian than OTL (perhaps up to 10%), but no blond-haired *Chinese or anything weird except perhaps in some isolated mountain passes.
I'd say the geography of China makes it likely that language replacement in Southern China will be similar to OTL, and we shouldn't expect the indigenous southern Chinese groups to hold on much better than IOTL.
An open question is how Indo-European polytheism would combine with the ancient Chinese religion?
Anyway, I'm hesitant to make this into a formal TL, in part because so little is known of the Indus Valley Civilization (since its writings have never been translated), and I'd need to figure out how to shape it as well in this world, and then undertake around 3,000 years of history.
Still, some thoughts?