There are many things that can be turned as "threads on a cone".

1. screw extractors
2. buffing wheel arbors.
3. log splitters.
4. custom wood screws.
5. Tapered end mills.(OK maybe to heavy for most lathers).
6. Marble tracks with a router attachment.

There are probably a few more I'm missing. In any event great to see you have G33 working. There are not a lot of posts about using LinuxCNC for lathe work so it is good to see people using it here. One day I'd like to have LinuxCNC running on a machine or two, but that is way off in the future.