Shourobh is a very decent player but I think he's being a bit overhyped here. I think he'll have a harder time than Bijoy adjusting to international cricket, and will take more time becoming the consistent performer he may become. He's definitely better than Rocky from what I've seen but that really isn't saying much.
I'm not sure how much time he'll have to do that once Shakib returns and bats at number 3 or 4. If Nayeem manages to rotate the strike with ease against quality attack in challenging conditions, something I feel he's capable of doing once relaxed, he'll fit nicely into the other slot.
That leaves 6 and 7 for Shourobh. Unless Mushfiq fails over a long period of time, 6 won't happen anytime soon. Riyad takes time to settle in but once he does, he can finish with the best of them. Shourobh also takes time to settle in, so unless we have an extraordinarily superior international cricketer in him, it would be better to go with the more experienced Riyad IMO.
"O people, we created you from the same male and female, and rendered you distinct peoples and tribes, that you may recognize one another. The best among you in the sight of GOD is the most righteous. GOD is Omniscient, Cognizant." (49:13)