I found two additional items that were persuasive:
- a Sigma SA-mount USB dock and
- a 100-400 dg dn in native L mount.
The 100-400 is more of a beast than I prefer, but reviews are more consistently positive than the other long options available at the moment. I suppose an L mount dock would now prove useful too.. we will get there!
I'm still hopeful that a ~50-200mm zoom suitable for the s⁹ will be offered soon, but if not one of the SA options will serve as a shorter telephoto.