Rough calculation in conclusion section In my conclusion, I imagine what my results could imply for future developments. I want to emphasize my argument with a rough calculation. Is this allowed in a conclusion section?
Not best practice.  You would be better off having that in a section of the Discussion (at the end of the Discussion) with at least a paragraph of explication.  You can use an identifying subheader ("future developments", "economic implications", etc. within Discussion).  

Then in the Conclusion, I would stick to more of the traditional method which is to restate the main results. At that point, you summarize all your findings.  And then give a single sentence about the implications.  

I think this is better than opening a segue within the Conclusion.