Godfrey,
The practicality of your answer I agree with entirely. Considering the shortcomings of M6 and later viewfinders (and coupled with my way of seeing), makes it seem like the creation of such a lens would be a no-brainer. The 35/2.8 C-Biogon falls short in the evening, but remains a cult status for good reason. How perfect would that sort of performance be in a small 56 degrees diagonal lens, with an extra stop for moonlight hours on our evening walks home? I'm assuming its success, again, would be assured by that of the Nokton's, and the compact 50/1.5 C-Sonnar. At the very least, I posit the Rollei 40mm f/2.8 HFT was not the success hoped for solely because it was missing one stop. The M-Rokkor is now about $500. A T* 40/2.0 with Zeiss' typically extended warranty would no doubt be a top-seller even at around a grand (I'd buy two).
Just wishing...
Daniel