In the latest Ghostbusters featurette, not only does the cast and crew speak lovingly about the new and old Ecto-1, but we actually see a lot more of its upcoming in-movie history. I don’t think it’s going to shock people to know that Holtzmann (Kate McKinnon) is behind a lot of the changes.
Source: io9 – See the Creation of the Ecto-1 in the Newest Ghostbusters Featurette