Removing some of the sand from the Sahara and replacing it with sea water does seem like a pretty far out project on the face of it, but it may not be.
We quarry sand all over the world for use in concrete, mortar, highways, etc. Often, there is a greater demand than supply for sand. You might think transportation would be an issue, but consider this: We are currently remodeling the kitchen. When we went to pick out granite for the counter tops, we found that granite can be quarried in Brazil, finished in China, and then sent back to California for less than the cost of quarrying and finishing granite right here!
Why that is, I don't know, and neither did the granite broker.
There are some questions that need to be answered still:
Who would be the one to carry out this project?
When someone is affected negatively in one way or another, who would compensate them, and how?
What unintended consequences might there be from a project this big?
