For one thing zooms are IMHO more useful than single focals. It's not always that easy to move a step forward or back. The other issue is that a "perfect" lens would only achieve it's maximum performance in a very narrow aperture range. Finally the sharpening steps in the digital process can hide or emphase weeknesses.
In the end the qustion how useful a lens is for the needs at hand. I would pay 2000 USD for a 24-70/2.8 or a 70-200/2.8 but probably not for a single focal, especially as I normally use f/8, which I see as an acceptable compromise between factors like depth of field, precision of focus, lens aberrations and diffraction.
In the final outcome the question is about utility. The problem with the Leica lenses may be that they need sensors with very small pixel pitch for best utilisation and such sensors are noisy. With Rodenstock HR Digitars and their likes we have more flexibility as we can put them on cameras with shifts and tilts. A digital back with "Digital" lenses is just an investment that can be utilized far more flexibly than just another DSLR, even if that DSLR is the best ever built with the best lenses ever made.
Some people will buy the new Leica and it's lenses and I'm perfectly sure those owners will be happy.
Anyway, I'm still fascinated with the technology. I also admire Porsche, Ferrari and Formula 1, but I have a Toyota station wagon.
In happy posession of a 24-70/2.8, 80-200/2.8, 100/2.8 Macro, 20/2.8, 300/4 and 400/4.5 among other things ;-)
Again, we are talking about lenses that are probably going to be 3 to 10 times more expensive than their 35 mm equivalents and are not that bright.
I am 100% sure that Nikon and Canon could produce a near perfect 50 mm f2 for 2.000 US$. Now,would you buy one?