f/1.0 isn't only about low light conditions. The 50mm f/1.0 lens renders as any other lens due to the shallow DoF and wide angle of vision (fingerprint of the lens apart).
The last issue of LFI has an interesting article on this subject.
Erwin Puts explains and shows why and how lenses have improved in the last 30 years. New glasses, new technologies (raw materials, manufacture), new computer tools... all this open a new world of possibilities.
Lens testing again! (Jan 29, 2008) | Photography and image capture: the Leica technique and philosophy by Erwin Puts | Erwin Puts
The Noctilux is a design from 1969, manufactured from 1976. Then, Leica had problems manufacturing ASPH lenses (the previous Noctilux). The glasses catalogue has changed a lot in those 40 years...
Economic sense is a different story. The 75mm focal length, for instance, never was a best seller, and Leica already has two models (Summarit and APO-Summicron). On the other hand, the M8 presents some limitations related to focus precision... so old high-speed designs can be improved but I don't know if this must be/can be a priority now.
Another factor: the R system. Leica will put a lot of resources in its development and updating for the new R10 camera.