I think having the ability to export questions would be a useful feature. It would get us one step closer to having the lesson module fully integrated into the question bank. That unfortunately is not a simple task since the lesson module and the question bank diverged many years ago. as a result both support features that the other does not. (For example the lesson short answer questions support regular expressions and the question bank version does not)
I'm not sure about merging lessons however. I think that would be rather complicated especially when you d=add in things like activity completion, conditional activities and grades. I think if a teacher could simply export the questions / pages from one lesson and then later import them into another then wouldn't they effectively be able to accomplish the same thing?