Good catch, generally it ends when there is a change in the threshold, or in your case, a change in the step.

That is how it is usually done. In your case, it might look better to start the upper trim even with the step.

Maybe? Try it both ways?

Wow! Its really pretty. Try blocking it off with some tape and paper to help you visualize both shapes.

Yes the picture you showed would be an acceptable way to deal with this situation. Are there more steps not shown. What's was done there.

Before you commit to cutting your expensive material make a couple of templates out of scrap wood or cardboard and see if you like the angled cut. Did this material come prefinished? If so hopefully you have some of the stain on hand to finish the angled cut.