Nopixel[0], a roleplay-focused modded GTAV server built on the FiveM framework[1], has absolutely exploded in popularity during the past year. Many of the most popular streamers on Twitch are active on this server. Cumulative live viewership of these streamers is in the tens or hundreds of thousands at any one time. Looking at the top live GTAV streamers[2], almost all are playing on Nopixel or some similar GTARP server.
Rockstar is notorious for being hostile to modders. Since Nopixel has become such a phenomenon recently (and a huge cash cow for streamers and streaming platforms) there is a lot of talk among the GTARP community about GTA6. There's speculation about whether Rockstar will continue to turn a blind eye to modders, lock down their software even more, try to go after modders legally, release their own competing RP platform or something else.
As an aside, I'm somewhat surprised I've never read any discussion about Nopixel on HN before. I started by watching one popular streamer try it a year ago and gradually began watching several Nopixel-only streamers when I get the chance. It's goofy and rough around the edges, but there are wildly creative and entertaining people involved. It feels like I've been watching a novel form of entertainment emerge in the course of a year. In a certain sense, it feels more like the "metaverse" than any thing I've seen recently advertised as such.
[0] https://nopixel.fandom.com/wiki/NoPixel_Community
[2] https://www.twitch.tv/directory/game/Grand%20Theft%20Auto%20...
edit: clarified that Nopixel is a server built on the FiveM framework