Grand Theft Auto V didn't have get any additional singleplayer content added after its launch, however, Rockstar Games were planning some DLC once upon a time. It's GTA Online that brought an end to the planned DLC. Not only was the multiplayer mode infinitely profitable but required constant updates with new content.
Similarly, it's believed that GTA Online's success has resulted in their not being a new
Grand Theft Auto instalment for quite some time — that is, according to
an industry analyst's recent report.
Though the singleplayer DLC wasn't officially announced by Rockstar Games, we know that they were working on some thanks to a couple of dataminers (via
Eurogamer). We also have somewhat of an idea what it would've involved: zombies. Similar to what Red Dead Redemption had with its "Undead Nightmare" DLC; Los Santos would've apparently been remodelled to match an apocalyptic aesthetic.
"What Rockstar was planning to do with the single-player DLC can be compared to adding a whole new map expansion. They had plans to redesign 80 or 90 percent of the map to fit a specific theme - one of the episodes was supposed to feature a zombie apocalypse. Rockstar would make changes to the whole map to fit the zombie apocalypse theme."
GTA Online recently got a new update which added an explorable and interactive casino to the game. According to a Rockstar Games insider, this casino was also originally meant to be a part of singleplayer DLC.
"The casino was supposed to come to GTA 5 as single-player DLC as well as to GTA Online but as many already know, the single-player DLCs got cancelled thanks to the success of GTA Online."