By 2020, there will be 4 subs, two Ming class and two Yuan/Kilo class, but not sure if they would be enough as we also need to see how India and Myanmar progresses as well as the advancement of sonar technologies.
As for a blockade, we need to be prepared for it as there is huge possibility for future disputes, for example, there is a certain "gray area" along the Bangladesh-India maritime boundary where the hydro-carbons resources are awarded to Bangladesh while the fisheries have been awarded to India, there could be future hostility centering around this issue. Also, consider other issues like India's diversion of the waters of transnational rivers could prompt us to halt the transit and bilateral trade which will have huge impact on the North East States, this could make India to impose a naval blockade.