@Samin
Possibly Bangladesh Govt. would introduce some phase out method and would possibly accept the Old passports till thier issued validity and the next passport would be machine readable which will be stapled to the old passport for travel purpose.
That's what I have - an Old passport with a current New Machine readable Passport.
That should not cause any problem as far as your Travel is concerned.
Hope it helps.
Always Hopeful
Hopeful Canadian