I am not sure which of the 4 countries you belong to :-). Your idea indicates you are not Indian. Because, most indian may be willing to merge with Nepal and Bhutan, but not with Pakistan and Bangladesh.
Assuming that the USI you are talking about happens someday, it will not good tight for long. The resulting breakage will give birth to many more pieces than that got united.
India is far from 'united' even with it's existing states. It is by gods grace that the North and South are holding together for 60 years now.
