Fully agree with the sentiments here in terms of "you might not need this", and for many of us the Steam Machine is not really marketed toward us in particular. I think it's not marketed
away from us, though.
For me, I am considering it, depending on the price. I already have a small form factor PC that I run Bazzite on in the living room. The problem? There's some kind of hardware issue. Unfortunately, it might be the Intel CPU. It results in sporadic issues including periods of time where memory errors spike like crazy. I love the PC ecosystem for what it is, but here's the problem: without redundant parts, I can't reasonably isolate the problem to figure out what to RMA. It's not abundantly clear, because the problem is sporadic. I'd need to replace parts one-by-one. So I've just been working around it for now.
But the Steam Machine is sold as a single unit, and it already runs the KDE desktop that I'm used to using on my TV. (It's better than you'd expect, with a couple of tweaks, though I hope the SteamOS version that ships with the Steam Machine moves to a Wayland session as my TV supports HDR.) If I have a problem with the hardware, I can send it back to Valve. Even better, I kind of actually trust Valve.
So for me it totally depends on price point. I don't game all that much on TV, but I do want a box connected to my TV that can game. Plus, bonus points if it's able to achieve a better idle power usage than my current small form factor build. Plus, even better, the device ships with native HDMI CEC support, which is fairly rare on PC graphics cards, requiring very frustrating workarounds. This is clearly a potential killer option for people who want a living room PC setup for their TV.
(Aside: if you are wondering what the experience with using a living room PC with KDE is like, it's not too bad. You have to crank up the scale factor a bit, but with a Bluetooth keyboard and touchpad device, it's pretty easy to use. There's no easy way to support receiving Chromecasts, though, though there is Shanocast, but it's a bit sketchy. Funny enough, I believe Apple's AirPlay is less locked down and you can use UxPlay to receive AirPlay requests. I mostly just use Librewolf with some quality of life extensions like YouTube Shorts Block and Sponsorblock and the like. It is a little clunky but my previous weapon of choice was Android TV and it has been horrifically enshittified, so those devices are basically ewaste now.)
If they manage an under $800 price point and deliver on performance, thermals and noise, you simply won't be able to beat this thing in almost any dimension buying parts new to make a build yourself. It is significantly smaller than anything you can build, and it theoretically packs significant power per inch in the sub-$1000 price point. As long as you don't mind paying Valve, I absolutely think this is a potential killer deal for many use cases that will involve barely ever actually using Steam.
(But, despite the end of this article, it is definitely worth some consideration whether you really need one. Even if you ultimately decide you want it anyways :P)