Despite how different they are, PlayerUnknown's Battlegrounds is, in some ways, the new CSGO. It's the big Steam shooter du jour, and it's stolen Counter-Strike's realistic gun porn crown. But there's one thing CSGO has CS-going for it that PUBG doesn't: the ability to consume all other games, thanks to mods.
Go 4 The Kill is modder Kinsi's take on the idea of a battle royale game in CSGO. The map, which is set in a mountain range dotted with towns, is four times the size of Overpass, one of CSGO's largest official maps. This is possible because the map is broken up into quadrants by mountains. As you climb them, you transition into what's basically another map, albeit one that's still connected to the rest. This video by 3kliksphilip shows what that looks like.
Despite the clever map trickery, Go 4 The Kill (alternative pronunciation: "Gopher: The Kill") is still not quite on the same scale as PUBG or others in the genre like Fortnite and H1Z1: King of the Kill, as it allows only up to 20 players to squawk and squabble over chicken dinner, not 100. That said, the mod still pushes the boundaries of what's typically possible in CSGO not just with its map size, but also with other ideas and mechanics from battle royale games. You parachute in at the start of each match, you collect weapons and items as you go, you move between safe zones as a circle closes in, and there's custom HUD and UI elements to complement it all.
It's an impressively elaborate mod. If you want to give it a try, you can hop on to its community run server by signing in with your Steam profile on the mod's site.