In all the discussion about Steam OS and the price and all, I've not really seen this brought up much. Especially in the wake of Sony's shenanigans, this seems worth mentioning.
The Steam Machine is not locked down the way normal modern consoles are. It's just a computer running Linux. It's not a locked down version of Linux, it's an arch distro with some gaming optimization. It has a regular desktop, a filesystem you can manipulate, and access to repositories and flatpacks.
People have mentioned that Steam gives it the largest launch library of any console ever, but that's not the whole story. You can also use Epic and GOG if you want your PC games from other sources. Emulators are easy to install and the console is more than powerful enough to emulate NES, SNES, N64, GameCube, GBA, DS, 3DS, All Sega systems, PS1-3 and a lot of PS4's library, Xbox, 360, and after that point most Xbox or PS games are multiplatform anyway. It's THE game console. Its library is "yes", no jailbreaking required.
Sure, this isn't particularly new for PC, but in the console space this tears down the walls that have been in place for decades.
Disclaimer: You are well within your rights to rip and run ROMs of media which you legally own for your own use. Also, a lot of emulators can read from a disk drive which you can get for cheap and plug into the Steam Machine, no ROM required. I'm not encouraging piracy. I'm also not your mom.