The World Hub Alpha sign-up page says:
“The World Hub Alpha will allow users to easily edit and change default airports in Microsoft Flight Simulator.”
OK, so I can modify a default airport to better meet my particular preferences - perhaps by adding a building, removing a tree, changing an AI taxiway path, removing or re-aligning a runway, etc. This sounds good, but it does not mention any ability to share my changes with anyone else. It that mentioned in another post somewhere?