I think that BD itself would need to develop a lot more and have more than just a beach to offer in order to attract millions of rich foreign tourists every year.
Having a foreign only tourism zone is a good first step but we need the ability for foreigners to visit lots of other places in BD like Sylhet tea gardens, Dhaka and the Sundarbans. Very few tourists like to spend 1-2 weeks on a beach.
It will still be a good 10-15 years before the standard of infrastructure in BD gets to a level that rich foreign tourists feel comfortable moving around in.
Also having one visa for BD, India, Nepal and Bhutan along with the integrated transport network will allow those that want the diversity to feel BD is worthwhile visiting.