JTB Current Folder app has been updated for AutoCAD 2018.
Every time you want to open a drawing, or attach external references, insert drawing as block or want to create a block, you will have a Current Folder item on the left of your file selection dialog box (in the custom places area). This folder shortcut will dynamically change depending on the location of the current drawing you have open.
Free trial of JTB Current Folder is available.