Version 1.0.0 can pick rails and works when you have something in hand already. So far I don't see a way to pick paths, so that may not happen. If anyone knows a way to access the tile (not entity) under the cursor, I'd love to hear about it.
Version 1.1.1 is feature complete, and unless anyone reports a bug or has a great enhancement idea, will probably be the final version of Picker. Major thanks to Nexela for testing help and for the idea to piggyback on the "clear cursor" key.