And we don't know yet, but I am hoping for reliability. My gaming PC is a nightmare. Sometimes it works great. Other times, I have to sacrifice a goat to get the thing to work.
Today I had to disable dual band WiFi on my windows gaming machine because PoE2 has this bug when a group of mobs surround you, network latency suddenly spikes, but only if the network card works on dual band... Sigh.
I assume many issues like that will still exist on Steam Machine, as it's kind of unrelated to what's running the buggy software.
That issue cannot be a bug in the game, because the operating system should not allow a game to (by any means) produce that type of behaviour. So it's a bug in your OS, potentially the network card driver.
There are fewer of those on Linux but they still exist.
I assume many issues like that will still exist on Steam Machine, as it's kind of unrelated to what's running the buggy software.