You can already play it on PC with PSNow so it's not a big thing for it to get an actual PC release so many years after the game launched on PS4. I know this is just an experiment for them and it's not going to hurt them financially as the game has already sold so well. The ONLY thing I like about this is that it gives me a slight hope that if the PC version has some graphical or performance upgrades that that they make it over to the game on PS5 either with some kind of patch or an upgraded release. The game is still one of the best looking games released in the current gen on any platform and while they aren't likely to create higher end assets since the game is already several years old It would still be nice if maybe they rework the engine to get it to perform at 60fps or increase the draw distance etc.
I still don't think it'd be a good move to release 1st party single player games on PC on day 1 and I don't think they will. While it won't kill my enjoyment of playing the games on PS5 I still worry about Sony changing the kind of games they make to fit the PC model better, I doubt they would but it's something that would be a huge mistake if they did. If their goal is to attract PC players to their ecosystem they'll need MP games since single player titles don't give anyone a reason to sign up to PS+
Oh well if you are a PC gamer and haven't played this game on a PS4 yet and if it does end up coming out on PC you should play it, it's a great game.