Its pretty simple really...we will become a Security Council Member with the Veto when we surpass the US on a nominal GDP basis, by then we should also have an effective nuclear Triad. In this world in the future the power between nations is going to be measured economically more than militarily.
I think the forecast for this to happen is between the 2030 to 2050 time period depending on the pace of our economic growth.
I think your timeline is somewhat correct, however economic power is only part of the equation.
India needs to make friends in the world. It also needs to start developing its own technologies and innovations. So long as the next Microsoft/IBM/Intel or Apple is American then America will be the leader of the world. India will not be powerful just because it has a large economy thanks to its large population.
EG see what happened to China in 18th and 19th century. It was the largest economy in the world but it was no match for the Western powers.
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To be worthy of a permanent UNSC seat India needs the ability to project its power. There's no point of having a seat if we can't contribute to international security because of our power projection limitations.
EG if the security council created a mandate to stop a foreign war on the other side of the world who can enforce it? At the moment there's really only one country that can, America, and a few countries that can contribute in a meaningful fashion: the UK/France.
When India has a few supercarrier battlegroups in its arsenal then it would be a useful addition to the UNSC, until then what point does it serve aside from aggrandizing India's own nest? That's my impartial view.
UN is a useless organization which never get anything done or pass, all the UN resolution pertaining to any particular nation that will strong object by the nation involve, then particular nation will curry the favor from the P5 nation to vote down the resolution. Never ending debate, bickering over decision, fighting to defeat the resolution without any mutual agreement among the nation in UN.
IDK, I think the UN has served its main purpose (to stop major power wars).
It was never intended to be representative of the whole world, hence most of the power of the UN is concentrated in its founding members.
Really the UN is the P5 nations, a UN consisting of just those Nations would be just as effective as the current UN body. The voice of Kenya, or Nigeria doesn't matter in terms of world affairs or world security. Kenya and Nigeria are at the whim of the Western powers and increasing China, as all nations are.
In 20 or so years China might start to rival the US, then in another 20 years India will join them. So perhaps we could add India to that P5 group then, but anymore nations than this is superfluous.