It should come as no surprise that the content that was added to GTA Online with the Cunning Stunts DLC has since made it to single player thanks to the work of modders. The modding community supporting Grand Theft Auto 5 have been pretty vigilant about adapting the content of the Online DLCs to single player, when possible.
GTA 5 has stayed pretty much the same as it was on launch, barring a few of the early Online DLCs adding content to it too. However, most of the truly beefy content updates the multiplayer portion received over the years stayed out of story mode. As insane as it must sound, there are actually players out there who prefer a solo experience but have already seen everything there is to see in GTA 5.
These are the players to tend to start modding their games, adding new content, game mechanics, missions and items to the experience to extend the playtime. While some have no qualms about going off the hook in the name of fun, playing with mods that add the Iron Man suit, or subject the world to a monarchy ruled by monkeys, others prefer to stick to lore-friendly mods.
In fact, some are so adamant about being lore-friendly, that they only mod items, missions and vehicles into the game which have already appeared in the GTA franchise as canon. This gave rise to the trend of creating mods that bring Online DLC content to story mode.
Now, obviously some things like Adversary Modes and new job types don't translate well to single player, so sometimes these mods stuck just to the vehicles. The most recent Online DLC, Cunning Stunts, added a whopping 13 of those and solo players were eager to get their hands on them.
A modder team comprised of _CP_, mockba.the.borg, sjaak327, WildBrick and robi29 delivered on that and then some. Recent updates to the game messed with vehicle spawning in single player, essentially breaking all older Online vehicle mods. Their newest project, titled "mpstunt in SP" grew into something much larger than the name would imply.
Not only does this new mod offer players a stable and reliable way of spawning modded vehicles while playing single player (any use of this mod or anything similar in GTA Online will ban your cheating ass), but it includes all the vehicles of recent DLCs, including Cunning Stunts, Further Adventures in Finance and Felony, Lowriders Classics and the various one-off vehicle mini-DLCs in between.
The team is planning on expanding the mod with further DLC vehicles, both in the future and retroactively. The mod is fairly difficult to get running, so if you're not too tech-savvy, get ready to embarrass yourself in the comments pleading for assistance.
In spite of the constant updates Rockstar is rolling out for GTA Online, there is still no word on any single player DLC ever coming. Hopes for this are dwindling, especially when you take into account that there really isn't a business case for it in light of Online's success.
Would you prefer if Rockstar added the Online DLC content to story mode as well?