I like your proposal however I do not think that Awami league would agree. Pakistan already offer us a route to central Asia for entrance of our goods however Awami league ignored it. It's rather busy to please it's Hindu masters.
AL is only less than half the affair of BD politics. A country's life is much longer than a political party. The way AL is ruling, results in the next election may be reversed.
If not through Afghanistan/Pakistan, then how BD will purchase goods from a landlocked Uzbekistan? India has already reduced its cotton exports to BD because it has to fulfill its own internal need. When Indian economy grows more, there will be little export from there.
BD is now trying to buy this item from two central regions, one is in africa and the other is in asia. If it is central asia, then Pakistan can help us more than any other country can do.
By the way, BD govt has demanded to India to agree to a railway route to Pakistan through its land. It is all in the name of regional connectivity. This demand is additional to the routes India is considering for BD-Nepal/Bhutan connectivity. Even if we get the connectivity, then also we will need Pakistan to get us cotton.
I personally do not think, India will get a free connectivity to its NE. It will have to agree to our demands for connectivities to the three countries that I have mentioned. You will not like it when I say that this govt is doing much better to bring us out of our make-believe island world.
I think, to give India a route to Assam is a stupid thing when it is thought out independently. But, now the ball is in the court of India. It will have to give us the routes we are demanding. Otherwise, there will be a NO to its own connectivity with its NE - you can rest assured of it.