My guess (just walking into this conversation) is that the obstacle free zone/runway protection zone/safety area requirements would pose problems with regards to the buildings, etc. that are between the existing taxiway and the bay.

Though looking at the FAA air traffic manual (https://www.faa.gov/air_traffic/publ...section_8.html) and the runway separation requirements for simultaneous same direction operations I feel like I'm missing something based on the discussion upthread as using the very precise measuring tool in Google Maps it appears there's already sufficient separation (even though my brain says that can't be right)