Can recent developments improve the total synthesis of B-12?
Almost certainly, yes. Applications of modern organic synthesis methods have drastically shortened the synthetic routes for such previously "daunting" targets such as strychnine see Vanderwal, tetracyclines Myers  and pyrroloindole alkaloids Movassaghi, to name but a few - and recent efforts by Baran and White on C-H activation of alkanes have already yielded more efficient syntheses of many complex polycyclic terpenes. There is no reason to think that significant improvement could not occur for chlorophyll or B12. In fact, the absence of chlorophyll or Vitamin B12 from modern synthetic efforts represents a bit of a blind spot; it could well be that new chemistry could be discovered in the process. Although that 1,16 hydride shift by Eschenmoser will be hard to beat :-)