Ok, since our friend Yun does not seem to be very eager to start working on his own thread, I will pitch in.
1. The "Zarathustra" reform movement starts in the BMAC like in our TL. It turns the old deivas of the Indo-Iraninan pantheon into demons and the previously demonized asuras into gods, while moving towards a form of quasi-monotheism centered on Ahura-Mazda.
2. In our TL, the pre-vedic still deiva-worsipping nomatic tribes north of the BMAC (Andronovo-related in some way?) attacked the settled BMAC sites, probably weakened them enough to cause their fall and then went on to invade India and topple the Harappan civilization in the process. Here, the POD would be that the BMAC is sufficiently stronger than IOTL to stave off the nomadic incursions from the north thus saving itself and the Harappans too.
3. A fused BMAC-Harappan civilization eventually emerges after several centuries; say around 1700 BC.
4. The Harappan pictograms are adopted by both cultures and eventually evolve into a sufficiently developed writing system to put in writing the core texts (hymns) of the early Zoroastrian religion.
5. During the second half of the 2nd millenium BC, a fully monotheistic religion develops out of Early Zoroastrism, in the BMAC area or in the Indus valley, predating Judaism by 500 years.
6. This religion eventually spawns a martyred-savior centered heterodox branch around 500BC, which spreads mostly east and out-competes Buddhism and Jaininsm (I assume that India was eventually conquered by IE speakers in this TL as well, although slightly later and that the history of the Ganges valley remains pretty much the same).
....
100. China experiences a steam-coal-steel industrial revolution around 1500 AD.
101. China colonizes the Americas with the help of firearms and steam-driven Pacific-Ocean crossing dreadnoughts.
102. New China lands a Taikonoaut on the Moon by 1850 AD
Comments welcome.