Dhaka would eventually overtake Kolkata as Bangladesh develops farther economically,and that is only natural with Dhaka being the country capital and priority number one. All showcase projects would ultimately end up in Dhaka.
That being said Kolkata at present is ahead of Dhaka, and outskirts of Kolkata are developing more rapidly than Kolkata. And Kolkata has all the basics in place- mass transport,important industries, planned suburbs, IT parks, world-renowned educational institutions. Dhaka should have to sort this type of things out before it can surpass Kolkata. And mind you Kolkata is growing as well and investments are pouring in albeit at a slower pace but still pouring in, because we have the base ready.