The optical properties of old classic lenses won't likely be replicated in the near future or ever, for that matter. Lead, Lanthanum and Thorium glass production was halted as of 2001. For example, the 38mm Biogon in the SWC underwent a slight formulation change due to the new glass restrictions. Most of the heavy metal glasses were phased out in the late 70s and 80s due to environmental and workplace hazards.
So there's one reason.
But as far as Leica goes, they have staked their claim into the digital realm. They can't reissue older designs due to the restrictions of the digital sensors and the very short lens registration. 27.8mm. DSLRs don't have this problem nearly as much since their lens designs force their lenses shorter than about 55mm to be retrofocal, which is a completely new lens design. Leica is heading this direction these days because their superwides on the new digital bodies are no longer flag vignetting. Yes, this is partially a function of computer correction via lens coding but it is also due to Leica designing the nodal point of their new fleet of lenses farther forward so the light rays are more perpendicular to the sensor. Look at that new "21mm Super Elmar f/3.4." They even made the maximum aperture the same as the classic Super Angulon, probably just for nostalgia but the lens is in a completely different class with regard to design. The rear element doesn't project nearly as far and the formulation forces light to leave the lens very perpendicular, as opposed to how the corners of the superlative Super Angulon behave with light rays projecting at very sharp angles onto the film plane. That just doesn't work on digital very well. The same goes for all of Leica's past lenses shorter than 50mm. Without coding, you'll see flag vignetting. If you want the same excellent design, like the Mandler 28mm Elmarit. Version 1 has the same rear element problem, so you can't use that amazing lens on what Leica sees as their future, without workarounds and image compromise.
A 66mm ELCAN could certainly be done but it was a special, rare, niche lens which never was intended for use by the general population. Design, raytracing, tooling, sourcing glass, all would be very expensive and the sales wouldn't pay for the investment.
Phil Forrest