Well, I suggested for their full independence not merger with Bangladesh. I've never been to North East India, but the Assamese whom I met here in Bangladesh, have high regards for the country. And actually being a Bengali is a crime in the North East, not Bangladeshi!
Haven't we discussed this matter before? They are proven Indian citizens and mostly from West Bengal, quite natural, WB is a densely populated area so people will obviously try to migrate in the less populated areas of the country, most preferably North East India. Now if the situation is so worse, the central government should start building inter-state fenced boundaries that would resist the demographic changes that the North East Indians are complaining.
All in all, the solution to every problem of the North East India clearly lies on their full independence, nothing else.