While I've not ordered one myself, I have noticed at least 5 of my friends putting down the deposit - compared to the total number of 0 people I knew who got the Steam Machines, it looks like theres a lot more hype behind this.
As a Linux gamer, I can attest that Proton is pretty great and people should expect a much better experience compared to that of the Steam Machines - the native Linux ports arent great.
Valve are also the ones taking on responsibility for game compatibility, so there shouldn't be many instances of having to rely on a dev to make their game compatible.
They keep talking about how anti-cheat games will work OoTB on launch, but I'm more curious about the Media Foundation issues that Proton still has - this is the big hurdle for me as a lot of Japanese devs use .wmv's for videos, which currently only work sometimes in Proton.
Though, once anti-cheat and Media Foundation are both addressed, Proton will have better compatibility with Windows games than even Windows does.