I can answer your questions about the Double Natural Spin.
No, it's not a syllabus figure, at least according to the ISTD.
Yes, it is the mirror image of the Double Reverse Spin. Once you've mastered the DRS, you'll be amazed how easy the Double Natural is to execute - for the lead, anyway. My partner had some trouble with her part.
I also noticed that the Hover Cross would be a borrow from Fox Trot and I'm very curious about what the timing would be in Waltz. Just have to try it, I guess (which is a big part of the fun of ballroom).
jj