Establishing a common currency is the final stage of regional integration. Are we there yet? We haven't even embarked on the first stage yet.
As I said, there are lots of issues that need to be addressed first. There is a fundamental conflict of interest - while Bangladesh focuses on economic diplomacy, India aims for power projection. They have territorial disputes with Pakistan and China which can develop into a small scale conflict any day. India's military expenditure is above 2.5% of GDP while that of Bangladesh is less than 1.5%. India's gross debt is more than 16 times higher than Bangladesh. All these issues have direct impact on monetary stability. Are we ready to pay for India's debts and power projection where we have nothing to do with?
EU's success with Euro and other regional initiatives is largely a result of US taking care of their security which allowed them to focus on economic development and social welfare. Similarly, India has to give up its Super power aspiration for any regional integration to be feasible here.
Besides, nationalism has to be toned down, or rather be eliminated, to initiate a successful regional integration. With the rise of Hindutva in India, I don't see any possibility of a such an integration with India.