SteamOS has a unique problem that no other ecosystem has to deal with: In order to leverage steam's strength, the size of the community, they had to do two things. First, ensure that the catalog of games is playable on the TV, and second, that this userbase can interact with the steam community on PCs. If the system can't do this, it requires a huuuge shift of users in order to make it successful, which requires the kind of investment microsoft did with the XBox.
The second bullet point above leads to an interesting problem if they go down the path of interoperability with PC clients: controllers and mice. PCs have several genres that are unplayable with a controller, and the mouse and keyboard combo offers a significant advantage in almost every kind of competitive gaming and multiplayer. I hope that their controller bridges the gap, and chances are it might.
The touchpad-based movement is a huge change from a joystick. Precision movement on a touch-style pad like that is the only way a controller could handle snap turns and accuracy that muscle movement on a mouse pad offers. The way its set up, I'd expect it to work sort of like the Thinkpad nib. If it works and people adopt it, it will allow people to play things like RTSes, turn-based games like Civ, and a host of other options. Yeah, hotkeys are another important point, but one more easily overcome than the massive gulf that currently exists between the mouse and the analog joystick.
There are other factors that will tie to its success, but I think the future of the system ties to its interoperability with the PC gamers. If it doesn't, its just going to be an also-ran.