It is unconfirmed (not anymore CONFIRMED HERE) whether or not this is a recent change, but on the Japanese portal site for Final Fantasy XIII, and its sequels, the Steam logo can be seen along side the Xbox 360 and Playstation 3 (in case that is taken down, here is a picture of the site). Also, on the North American page for Final Fantasy XIII, a listing for PC can be seen (again, image here).
This is not completely far-fetched, as multiple Final Fantasy games are on Steam already like Final Fantasy VII and Final Fantasy VIII. Though those had PC releases before Steam as well. S
Square Enix has also expressed in the past that they would like to put more Final Fantasy games on Steam. Given how they have continued to create games based on Final Fantasy XIII, it is not unimaginable that they would like to spread it around some more.
What does this mean for the future? Who knows. Maybe Square Enix will toy with the idea of releasing future games on PC in the Final Fantasy series. This may be a trial run to see how things would go given that the third installment in the Final Fantasy XIII line, Lightning Returns: Final Fantasy XIII, only came out this year. This is of all course predicated on Final Fantasy XIII coming to Steam or PC in some fashion in the first place.
Before Final Fantasy VII showed up on Steam, similar rumors started to spread with similar information. Of course, Square Enix denied it up until they did their own announcement. We’ll see what they do here.