It seems a bit pointless, Steam users love steam because of the flexibility using a PC provides, plus you can easily plug up a PC to a TV and controller already, so I doubt it will haul in any PC gamers.
Console gamers are comfortable with existing brands to will most likely not give it a second glance.
I know you can build your own Steam machine, but wouldn’t the effort and money be better invested in building a regular desktop.
Finally lots of Steam games need a keyboard and mouse(Strategy games etc ) and most PC players prefer a mouse for shooting games.