I'm not sure if you understand what the Steam Machine is. In any case, it's not a “proprietary PC”. It's a PC running a full-featured Linux with all its capabilities. However, it's also not “just” a PC running Linux with Proton and Steam. Since everything comes from a single source (Valve), all components (hardware and software) will be very well harmonized.Last thing we need is yet another proprietary PC pretending to be a console. That's all the current console generation is anyway, just PCs with extremely limited interfaces. And we need another one named Steam Machine?
But no one is forced to buy it. But I find it a fascinating idea, and I'm not even a big gamer. But that's exactly what I find interesting: having a “console” for the living room or desk that also offers full PC capabilities. And if it brings some people closer to Linux, in my opinion, all the better.