He won't say whether it is worth $4000 to me, but I will. Me, neither, but if they release a 24mm, as is rumored, then I might consider it. It would have to blow away the TS-E 24mm, though.
If you shoot 55mm all day long (think fashion or advertising pros) and do huge enlargements (think fashion or advertising pros again), I think this lens would probably be worthwhile. For the rest of us, no.
I think the target market is not pros (who would be better served by the Canon 50L as it has AF, or a medium format system if they really need the resolution), but enthusiasts with lots of money who really need the 'best lens in the world' for their holiday snaps.
This also is the power of Leica IMHO.
5D3, 5D2, Sony α6000, G16 | EF: SY14/2.8, V20/3.5, 28/2.8 IS, Ʃ35/1.4, 50/1.8, 50/1.8 STM, Ʃ50/1.4 EX, 100/2.8L IS Macro, 16-35/4L IS, 24-105/4L IS, 70-200/2.8L IS II, 1.4x II, 2.0x III, T28-300 VC PZD, 70-300L IS, Ʃ150-600 OS HSM S | E: SY12/2, 35/1.8 OSS, 16-70 ZA OSS, 55-210 OSS, SY300/6.3 ED UMC