These things should be timed. Beating the Executives and Other Criminals single-player port mod in terms of turnaround time, the new custom rides introduced in the newest GTA Online DLC, Custom Classics, have now been added as spawnable vehicles in single player thanks to a mod.
GTA Online has been seeing fairly frequent free DLC updates ever since it was first launched soon after GTA V back in 2013. However, unfortunately the game's solo portion has remained unchanged and thus un-updated ever since launch. Aside from bug fixes, the story mode of the game never saw official new content.
It wasn't until the release of the final port — the PC version — that this would change, at least partially. GTA V on PC supported the use of third-party mods, allowing players to expand their single player experience for the first time. Once modding caught on, it wasn't long before DLC content was being ported over for solo players to enjoy too.
