While it's already known that the Steam Deck will ship with Valve's own SteamOS 3 based on Arch Linux, what about running more standard Linux distributions? It will get easier in a future version of the Linux Kernel.
Since it's open source, Linux gives Valve a lot of true control on what they can do and tweak for the Steam Deck and that's a big part of the reason they went with Linux instead of Windows. At release it will likely be using a good number of Valve special patches, many of which will be upstreamed to various projects and we're starting to see part of that now.
Sent into the Kernel mailing list was this patch across the weekend that adds in a driver to expose various low-level features of the Steam Deck including (but not limited to): the CPU fan control, Read-only access to DDIC registers, Battery temperature measurements, Various display related control knobs and a USB Type-C connector event notification.
Having it upstreamed isn't just good for other distributions of Linux though, it's less hassle for Valve once it's all official as there's no messing around with patches.
Hopefully this will all be pulled in and ready for Linux Kernel 5.18, which would be due out quite a bit later this year.