Nominal GDP growth rate is close to 15-20% a year could get you to $5 trillion dollar mark. Besides after certain period taka will gain value like chinese yuan. There are lot of things you need to take in consideration. I dont think $5 trillion dollar economy too unrealistic when Japan has a GDP $4 trillion dollar with half the population of BD.
With a 128 million people Japan's GDP is $4.4 trillion. This is something even a very well developed economy like South Korea cannot dream of emulating in per capita term. With a population just more than 50 million South Korean GDP is about $1 trillion. Rather, both the economies of Japan and South korea are falling.
Because Japan did, therefore, a half educated country Bangladesh can do it is a flawed logic. Note, Japan reached a 100% literacy sometime in 1905. Japan has been building its own industries, factories, railways, roads, river bridges, sea bridges, expressways, dams and subways by itself. Japanese are doing all these heavy constructions by themselves, and some, such as its 1st Tokyo subway, before WWII. What is BD's track record? It is nothing or almost nothing.
Japan never sought foreign loan except one time when it planned to build its 500 km long TOMEI Expressway in the '60s. It borrowed some $500 million from propbably UN, but returned the money before the due date. Japan did not develop by begging from others. In comparison, what is our own status?
To know and understand Japan, one has to come and see the industries of Japan. After living in Japan for many years, I am still surprised to see all their huge mills and factories, their transport system, road, railway, shipbuilding, IT and many many other things that have together made a country called Japan. German and France together is not equal to Japan.
When the installed capacity of electricity in BD is only 4000 MW, Japan's capacity is more than 250,000 MW. Is there any country that can churn out industrial/consumer goods without the infusion of electricity? So, ask BD govt to raise the installed capacity of power to just 25,000 MW. Do you have any idea how long it will take for a big talking Bangladesh? Check the track record, it will take a minimum of another 30 to 35 years to reach that point.
It means, it will be already 2047 when we will be producing only 25,000 MW of power. So, now tell me how you are going to produce a $5 trillion worth of goods and services at that time or in 2050 when the available power is only 25,000 MW.
So, do not please talk about Japan when you talk about BD. Every country has a different history of economic development. Yet, all the developed countries have some similarities. But, I do not find our people have any affinity to the mindset of any developed country. So, I believe, our country will make a few pockets of development, but, basically, it will remain almost poor a country with far far less than $1 trillion GDP. Note, this is what the South Korean GDP is today.