Here is the link which is quite old.
http://www.thedailystar.net/news-detail-209285
My two cents on this is that Chars (riverine islands) maybe cheaper and easier places but they don't make great structural places to build things on. Chars are brand new land which are hardly stable.
Whereas the land in the Barind areas (Varendra areas) near the National parks north of Gazipur and near the BIPSOT training grounds is far more suitable because of stability and firm substrate (the best we have in our little homeland).
Look at how Kansai airport had land subsidence and sinking problems which became a problem even decades after being built.
http://www.askcaptainlim.com/airports-aviation-33/23-is-kansai-airport-sinking.html
They were able to arrest the sinking which was very costly. We are not Japan and we don't have billions to spare like they do unless absolutely needed...
Also - look at how they are adding another island - you have to give some props to these people. It takes balls to landfill the sea at Osaka bay (60 feet deep) and then build something like this...
Yes IMHO Kansai can be the model for Dhaka's new airport. We need space for expansion in another twenty years after it is built...
Well Bangladesh cannot become Malaysia overnight but it can't remain where it is for long. People are too well exposed to KL and Bangkok nowadays.
Comilla Mainamati near the Cantt. could be great as you say as that area is not too well populated. Placing airports too close to water has issues - you have to build marine walls to stop ingress of water during river tsunamis or hurricanes. Kansai spent $1 billion in raising the airport. It is not cheap.
Don't shoot me because I have an opinion.
We have to rise above regionalism because practically speaking the DAC-CTG land and rail corridor is where EPZ's will have the greatest logistical success because of ease of freight shipping. The airport can be in the middle of it. Or about within 40 Miles radius of Dhaka in any other direction.
Our DAC-CTG Corridor is equal to China's EPZ's strung across it's west coast.