Landscape Architect

The tools will work on both runtime and in editor. The changes you make can be saved to disk in a binary file. I have it working on runtime now. For editor a bit more work is needed, as that binary data needs to go in a uasset file so it can be cooked

As for the save system itself, it is fast enough (Loading: O(1); Saving: O(N) in worst case and O(1) in best case, where N is no. of existing chunks saved in disk).