We recently reported on the big project of OpenIV, when the team announced to release a mod for GTA V, where you can enter the entire map of Liberty City, imported directly from GTA IV. This mammoth project is likely to devour a lot of time, as the city will be not only accessible but also animated. Cars, pedestrians, etc.
In fact, the OpenIV team is sure that a release should be possible in spring or summer 2017. First screenshots show the city and buildings, as well as the view from the coast of Liberty City with a view of Los Santos.
To install the mod, you still need a fully-fledged version of GTA IV, because the card is imported from it. Thus one tries also to avoid disputes with Rockstar, as far as copyrights are concerned.