cheapchips
Veteran
The support for third party linux applications (and app stores) sounds a bit scary. Unless they use VM or container isolation it will be hard to keep the core Linux install secure. A VM solution will be awkward without multiuser GPU drivers from AMD (which they don't currently offer for consumer hardware, unlike Intel). Even with containers they have to be careful with say X-windows isolation.
Just going letting people install any Arch package they want for the core OS is a recipe for disaster.
I'm fairly ignorant when come to Linux. How is SteamOS scarier than any other flavour?
You presumably have to exit Steam's Little? Picture Mode and expend some effort to leave Valve's ecosystem.