MP (online) cars to SP-mode traffic
I wonder if there's any mod that relates to Online cars being in Singleplayer as NPC traffic cars. That would be nice to see something new in the LS traffic of story mode.
Several mods change the population cycle to include DLC vehicles. I'm currently not up-to-date with each of them, but at least VanillaWorks and its derivatives always seem to include it.
Southern San Andreas Exotic does something similar but with add-on cars
I'd do it myself if I were you. That way you take control over the modding. And choose which vehicles from online you'd like in what zone (city, rural, freeway, etc)
Just use an editable popgroups.ymt and add the newer modelnames from the patchdays to each zone