Since Hawaii will still be permanently maintained by me, I think it is safe to keep those achievements in-game - collectors can easily opt-in to the map from the menu. In the future I intend to make the opt-in/out process smoother as well. Germany will be the next map to retire.
Edit: To clarify, Germany’s map files will be retired to the workshop, but the assets will remain in the vanilla game files permanently. A new system for workshop asset dependencies will also be introduced in the future. (Wanted to avoid Germany asset panic!)