1. Steam OS will be powered by Linux + OpenGL
2. It will have unparalleled gamer-bias and developer-bias instead of revolving around publishers (meaning its truly gamer focused as what has been Valve's MO)
3. It will be just good enough in the graphics department but will instead lower the friction in the assets pipeline department, virality and player-analytics
4. Graphics will now take a backseat to story, AI, art-direction and pacing (due to the hardware spec being fixed and player measuring tools)
5. crowdsourcing features will be baked in thru APIs (Team Fortress hats as a precursor)
6. social multiplayer features baked in thru APIs
7. a standard controller will be mandated
8. optional accessories like bio-measuring gadgets (measure opponent's sweat, heart-rate and track gaze) will be sold online.
If any of this comes to pass then it would have made PC gaming much much more evolved.