An RP server isn't just a different rule set - it's a different version of the world. The custom locations a server ships are how that world becomes specific. We work through the mapping side of RP here.
For the player-facing RP question, see the RP server expectations piece.
What kinds of custom locations RP servers ship
The standard pack: police department interior, hospital interior, mechanic shop interior, courthouse interior. Then per-server differentiation: clothing stores, tattoo parlours, drug labs, custom businesses, faction headquarters, housing, social hubs.
Most of these are MLOs - custom interiors loaded at runtime. Some are exterior modifications - new buildings dropped into existing parts of the map.
How RP mapping differs from single-player mapping
Server-shipped, not player-installed. Designed for many simultaneous players, not one. Has to integrate with the server's economy, jobs and faction systems. Has to support concurrent NPC and player activity without breaking immersion.
Server admins commission MLOs from creators rather than ship them themselves. The MLO marketplace exists because of this dynamic.
What this looks like for GTA 6
Speculative but reasonable extrapolation. After the PC release and the framework arrives, the standard pack of MLOs will be ported or rebuilt for GTA 6. The MLO marketplace will follow. Faction-specific custom locations will emerge as servers differentiate.
First serious RP server mappings probably stand up within a year of PC release. NoPixel-tier polish multiple years out. Server-side, the practical bit a lot of new RP communities forget is hosting - GTA hosting setup guides cover the requirements and trade-offs that actually decide whether a heavy MLO pack runs cleanly under load.