Why would you need a new manufacturing facility for RF lenses? Although the mount allows for new and better optical formulas, the components are all virtually the same. Same glass production, same motors, same barrel components, same assembly, even if the optical formula is different.An EOS R pro, would want the bread and butter pro lenses to match - if we are expecting a R pro in 6 months these these new pro lenses at 12 -18 months off seem unlikely to me. Unless proven new lens tech need a new manufacturing facility set up to produce them.
Regarding the slow sales of the R - sure i see that for working pro's, but for tech fans isn't it still very desirable body especially with the 28-70mm F2. I know i'd want to shoot with this combo loads if possible.