Canon had an EF 100mm f/2. An RF 100/105mm f/1.8L IS could be an upgrade (just like EF 135mm f/2L to RF 135mm f/1.8L IS) and an extension of the VCM series using the same barrel and filter size as the f/1.4L members do.
Which was and still is excellent, according to a recent review by OpticalLimits .
Quote:
"The Nikkor P.C. 105mm f/2.5 may be 50+ years old but it's still an impressive lens even by today's standards. Especially the image sharpness is impressive. And it's not only about the center quality - the lens is quite evenly sharp across the image field at f/2.8"