You know what would be funny but also genius if done right? If Valve releases Half-life 3 on the release of the Steam Machine.
Since I noticed a pattern that might actually be genius if they do it. Valve's games always try something new in each game they make; they utilize the full extent and potential of a medium to enhance the gameplay and the stories as well. Each game is basically a tech demo.
But over the years, they probably ran out of ideas to add in the limited PC medium or they were too ambitious that gameplay would be difficult in PC.
So they used another medium like VR with Half-life Alyx, they were able to bring their visions to life with the use of another medium.
But now with the Steam Machine, they are given a new and versatile medium. Using the full extent of the Steam Controller would be amazing; the gyro and track pad utilized to its fullest potential like how Nintendo uses its console's features would be amazing.
HL3 would probably be just one big tech demo of the Steam Machine's capabilities and adding it along with its release would be the biggest marketing stunt of all time.
This probably opens up a lot of things to Valve, letting them dip their toes into the console games industry and probably compete with Nintendo.