Congrats on Godot 4 Beta, it looks stunning! Though I would like to suggest to add simple features to path2d (and 3d, why not) like one point curve closing. When a user clicks on "close curve" it would be fantastic if there's an option to make it complete loop curve (with one point) instead of starting and ending points just sitting on top of each other. It should also enable in and out handles mirroring on closing point.
The second suggestion would be to have a tick option to make the path2d/3d visible in game mode. Optionally the points (and in/out handles) could be visible too. That could also enable the developer to select and adjust the line in game mode.