I highly doubt Valve, who had to fight with Microsoft to make a massive content update for their game available for free (and, hell, just gave away a full multiplayer game for free on PC a couple of months ago), would start charging for multiplayer. Epic seems slightly more likely, but still highly doubtful. It's the massive companies like Activision, UbiSoft, and EA that I'd see doing this sort of thing, and EA would probably only do so in their sports games.
I do see Activision charging for online in their rhythm games if they go through with all this, because they're that greedy. They wouldn't be exploiting those franchises to their fullest extent if they didn't charge for online, you see.