Eh, they're kinda muddying the GTAO content vs. GTAV content in that press release. While vehicles, guns, outfits, and some other items made for GTAO are available in single-player GTAV, not all content is, so "new jobs" and "properties," for instance, aren't in single player GTAV.
Hoping for a more proper announcement from Rockstar on single player content in addition to the port. At this time in the GTAIV release cycle, Lost and the Damned was about to release and Ballad was 6 months after that. For GTAV, it'll be a year+ after release without any noteworthy single player DLC on the horizon. I know they have priorities (GTAO -> X1/PS4 -> whatever elsE), but hoping a decent single player pack is part of that... not the scale of Ballad or L&D, but something.