I actually thought about it some time ago, but decided to go with a single rating for video games. The reason was that 1) it would create some redundant data and complicate the matter, and 2) if you sell similar but different products under a certain name, you better do all the versions good, or the name will be hurt. Going that way, we could start rating websites differently under each browser or device, or rate movies in both 2D and 3D. May be too much.
Still, OpiWiki ranks system would allow to get the average rating for the game (from all platform-versions), so No.2 is not really an issue. You can create a new voting, here on Meta, and ask users whether they want multiple platform-ratings for games.
The PC, Playstation, Xbox, etc. (games) rankings are useless on its own. The point is that in the future it will be possible to filter all game rankings by those ranks. For example, an user will be able to filter the RPGs ranking by the platform rankings.
You can add rankings such as PS4 games, etc.