I can see several different niches for it.

• PC gamers who want an HTPC. Which isn't really a niche that is served without building an ITX machine, with parts that are premium priced for no reason I can think of. If you want to play some of your PC games on a television, well, there aren't a lot of great solutions.

• Console gamers looking to convert. Consoles have come up in price significantly, the "turn on and play" aspects have eroded to the point a console is a slightly discounted mi-tier gaming PC that can't spreadsheet. The Steam Machine will be at a little bit of a price premium, but you get a console-like user experience with all the benefits of the PC ecosystem, like mods, streaming, self-hosted multiplayer, etc.

• IT professionals who just want to play games in their spare time. I've heard a lot of sysadmins and developers and folks rage at the idea of coming home from a long day at the IT mines only to futz around with PCIe lanes and EFI settings. The most hacker dude I know showed me his personal phone: a non-jailbroken iPhone.

• Noobs that are sick of Microsoft. There's people out there who would like a gaming PC without Windows, but for one reason or another can't move past the need to buy a computer with an OS installed from a for-profit company.

• Parents buying kids a gaming PC.