Sony has already confirmed that the only games that require PS Plus use Sony's Servers, i.e MMOs do not.
The only reason PS Plus is need for multiplayer is because Sony spent the entire gen 7 competing with Xbox Live with a free service.
XBL has shown that gamers will pay for online multiplayer on consoles, considering the DOOM surrounding sony for the last eight years, it would be foolish for them to simply leave all that money on the table, because of Nintendo, especially when Nintendo is hardly competing with XBOX on that front.
In fact by keeping the Marketplace free and enticing people to pay with multiplayer they are best suited to profit from this.
In this day and age, with the Internet, ignorance is a choice! And they're still choosing Ignorance! - Dr. Filthy Frank