The course has remained almost the same since 1976 but originally there were 3000 runners. The Staten Island start was reasonable then.
Today with 50,000+ runners the course needs to be changed to make things easier for NYRR and the entrants in the NYCM.
Everybody would be able to get to the start on their own by taking the subway.
The 5 borough race would then become a 4 borough race. The finish line would stay the same as there seem to be no better options.