https://msfsaddons.com/2023/06/12/microsoft-confirms-msfs-2024-is-a-full-on-new-simulator-compatible-with-virtually-all-the-existing-add-ons/#:~:text=Microsoft confirmed that%2C with very,in Microsoft Flight Simulator 2024.
Apparently virtually all addons will be transferrable so in reality and practicality it's similar to buying a new module for GBS or DCS but without integration into current maps. However, unlike GBS and DCS MSFS covers the whole globe (sorry flat earthers) in one purchase not small portions that you have to buy each time you want to fly somewhere different as in GBS and DCS. In some respects, for those that like the genre and are looking for a long term investment, it's probably better value buying '2024'.