Valve spokesperson told Road to VR that they’re not promising to support stereoscopic 3D for flat games but they are looking into it.
The company further said it’s considering a system-level implementation that could display any stereoscopic 3D content, whether it’s stereoscopically rendered games, videos, or photos. Should the stereoscopic 3D feature be built, Valve told me it would “be our goal” to be able to display such content when streamed from a PC or rendered directly on the headset itself.
Making something like 3dsen is a much more difficult task than being able to display a game that is using a 3d engine and so would generally be fundamentally capable of providing a stereoscopic view. That said, most of them currently don’t offer it anyway and it’s still not quite zero effort to add such a capability.
It does seem like Valve are saying they want to let you view a game in a stereoscopic 3D if the game has support for it built-in already so it would be 3d support for flat games (meaning games primarily made to be run on a screen) but only if the game has support for it. That’s good but does mean there’s still a need for either developers or 3rd parties to make the changes needed for it to function.