Looks great, so it seems we can insert a note at any moment during the design, that's a great addition! Perhaps the timeline root should always be a description note that cannot be deleted, then it will always be simple for shared designs to have a starting point to read about a design's capabilities, goals, printer settings, copyright's, website etc. Perhaps there could be a default template in the root note.
Currently you cannot delete the first step of the timeline, which is a strange limitation because it means I cannot delete the first object I placed in a design anymore. If the first step is a description note then that makes perfect sense. Just my 2 cents.