In their most recent investor call Take-Two Interactive announced they have managed to ship over 65 million copies of Grand Theft Auto V worldwide. The previous update on the sales number, made in February 2016, was 60 million – so yeah, they moved 5 million copies of the game in the last three months, two and a half years after the original release! If we consider the year-over-year growth, it amounts to about 13 million. Grand Theft Auto V was first out on Xbox 360 and PlayStation 3 in September 2013. The game was then ported to current generation consoles – Xbox One and PlayStation 4 – in November 2014. Finally, it hit PC in April 2015.
When asked about remasters of earlier GTA games that were first released on PlayStation 2, Take-Two CEO Strauss Zelnick said they “wouldn't do anything that's not going to look great creatively” (via GameSpot). This means the publisher won’t push Rockstar Games to do this, but if they decide that remastering those games is a good idea from a creative point of view, it may well happen. This would most probably mean a complete overhaul and not just porting them to modern platforms (which has already happened in some cases: see PS4 version of GTA III, GTA: Vice City, GTA: San Andreas).