They also confirmed this for the next one without having to say anything at all. Because you know it'll be in there from the start.

I think that's what rolling this out now is really about and why it isn't GTA V+, it's GTA+.

If they announce paid online in the context of being new with GTA VI's release people would be up in arms. But by adding it to GTA V they can limit the backlash and normalize this well ahead of the new game's release. And by that time gamejournos will probably be saying that not liking GTA VI because of it is "review bombing" (while they no doubt have free credit) because GTA V already had it.