I can attest to this, my business partner has the Merc C class PHEV and is one of those who still has the charging cable still in its cellophane in the boot. The only reason people are getting these PHEVs is the extremely low company car tax, once that's withdrawn (and it's coming) sales of PHEVS will implode, which is likely to affect manufacturer's investment in the technology. There is no magic bullet at the moment, I think straight diesel, and even straight petrol, engines are going to be with us for a good few years yet.