I think the fifth line is complete but not commissioned due to encroachment and political pressure. if we see the pace of work of extension of harbour line from andheri to goregaon which is not more than 7 km (10 years and still counting), you can easily believe that it is next to impossible to construct 6th line between bvi and bct. Rather than wasting time and money on other plans, WR should concentrate on overhead metro lines from virar to dadar, which will be easier to execute with minimum or no land acquisition.