Is 16 bit printing even relevant yet in Windows? I've read some about the newer XPS drivers which apparently support 16 bit colour depth printing but haven't found any good information yet on integration of the driver from the manufacturer and apps like PS or LR.
XPS print path has been around for a while (it was introduced with Vista, and even back-ported to XP). But nobody seems to be supporting it, probably because it's a completely new interface from the GDI that developers have been using for years and years.
Other than that, Canon has 16-bit printing plugins for their printers, available for use in Photoshop (but not Lightroom or other applications).
I agree there's no need for profiling test targets to be 16-bit color, even when creating 16-bit profiles for use with a 16-bit printing path.