Insh'Allah the union will happen. Indians and Bangladeshis in the local level don't really have a problems with each other; however, the Indian gov't blocks alot of Bangladeshi exports which is due to political decision by New Dehli.
However, I have talked to people in Bangladesh and they said Bangladeshis get along with the Pakistanis who are living in Bangladesh. Then I asked about the issue of war, and I was told the rising generation, the ones who will take charge of Bangladesh in 5-10 years, don't really consider much about the war. In Bangla I was told "ora shob bhoole gese" which means they all forgot about the war. Islam is gaining momentum in Bangladesh and freindship with Pakistan is increasing among the Bangladeshi people, and we can also see that on the government level.
Basically it's the political party Awami League who brings it up along with their nationalist supporters.
The union will benefit both Bangladesh and Pakistan economically and it'll be a great move in front of the Muslim world. As for including India, Bangladeshis wont let them in initially due to the ban on Bangladeshi products to India.
Ambitious Bangladeshis like myself are eager to ally ourselves with our Muslim brethren of Pakistan, "seb se pehle Islam".