Estimated population in regional countries by 2050:
List of countries by past and future population - Wikipedia, the free encyclopedia
ASEAN-10 million
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Indonesia 313
Philippines 172
Vietnam 111
Thailand 70
Myanmar 71
Malaysia 43
Cambodia 22
Laos 10
Singapore 9
Brunei 1
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subtotal 822
Proximal
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Japan 107
South Korea 43
North Korea 27
Bangladesh 250
Sri Lanka 25
Timor Leste 2
Papua NG 10
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subtotal 464
Total 1286
Muslim regional 540
China 1304
India 1657
Muslim(global) 2300-2800
How long can India keep Bangladesh population hostage under gun point? It is not sustainable. Its only a matter of time that Indian agents are defeated, question is how long.
What you mentioned about China, they are too paranoid to look at any regional alliance not as a threat, but if regional countries depend on each other, it reduces their dependence on outside offshore balancer, such as the US. That is the key point to understand for China, if they want to see reduced outside interference in the region.
But considering real politik, China will be opposed to these kind of ideas and the US will be for it and it can only grow under US/NATO/West umbrella.
When and if Japan makes a move, with US backing, India will have no choice but to step aside and let a sovereign Muslim country of 250 million (2050) people decide their own future and national destiny.