Lets be realistic here. Tibet will never be a gateway for exchange goods and people between China and India even if one day China and India will become allies. Not in the next 100 years, even in the next one thousand years or even ten thousand years. Its just a simple fact the Tibetan plateau, averages at 4300 meters. This even excludes the higher altitudes of the Himalayas range which acts as dividing wall between China and India. It takes so much potential energy to lift 1 kilogram of something in there, not to mention the kinetic energy needed to transfer from developed places below the Tibet plateau to developed places in Tibet plateau.
This is the reason why logistics to Tibet is poor over the centuries because of so much energy cost to move something with little return.
Majority of goods are moved on oceans over distances because the potential energy cost is zero.
Its very expensive to move 1 TEU container 4 km up.
China values Tibet for strategic reasons not for economic reasons.