The Steam Machine and Steam Frame are probably delayed, but they still intend to release them in the first half of this year.
They said they planned to have a concrete launch window and pricing by now, but hardware pricing/shortages have made that hard to pin down.
Not entirely the same, if the drivers are builtin into the Linux Kernel. I don’t know if the Steam Controller drivers will be Open Source, so maybe its the same.
It definitely looks like it’s going to be a standard USB HID type device, if their SDL support is anything to go by.