On PC, your game can become immortal with proper mod support and a creative community, though given GTA 5’s success already, anything that happens with the PC version is just icing on the cake. So Rockstar will have to not only fix that, but also figure out a way to make sure that GTA 5 does its best to be the next Skyrim on PC, an open world game with infinite potential given the fact that it’s the most fleshed-out sandbox currently on the market, and the possibilities for modders are endless. The best hack I’ve heard has players shooting other players with bags of money, forcing them to acquire billions of dollars, essentially negating the entire progression system of the game.
Despite their best intentions, PC GTA Online is still rife with cheaters and trolls, and many players have reported a downright frustrating play experience as a result. That, however, has been a difficult goal to achieve. Their only statement about mods to date is that they’re focused on ensuring that GTA Online specifically is a fair, fun experience for everyone. It’s possible Rockstar was waiting to see what happened there before announcing their own plans for mods, and now that it’s gone bust, that may throw a wrench into whatever plans they had. It’s entirely possible that they were planning on partnering with Valve for phase two of Steam's pay-for-mods store experiment, an experiment which has already failed spectacularly with the setting up and taking down of a paid store for Skyrim mods.
It’s going to be interesting to see how Rockstar reacts to their already growing stable of modders, as so far, they’ve offered no official support (and a recent patch has actually disabled mods completely). I believe GTA 4 had about 3.5 million lifetime PC sales, so GTA 5 has already done more than half that, and this is before the modding community has really taken off. GTA 5 will likely prove to have a lot of longevity on PC, and 2 million copies sold this quickly is a great start.