Linux

This is an old comment but I am replying anyway.

The idea of statelessness is not limiting user configuration but giving user a sane default config. Many software doesn't work without a config file, the idea is that a software should ship a default (vendored) configuration that make the software can be used as is. The default config is stored at vendored directory. This default config file then should be able overriden by user own config.

For example: Alex needs program "A" for work but program "A" needs a config file to even launch. Ideally the program "A" should ship a default config file to vendored directory in /usr. If Alex needs to modify the configuration to fit his needs, now he can do that by copying the default configuration in /usr directory to either /etc (system wide) or /.local/config (per-user). Alex now can modify the config file as he pleases. Now, in case some modification Alex made make program "A" doesn't work, he can just nuke his own config file and program "A" will work again because of the default config is there as a fallback.

Good news is many program is already following this schema of configuration files but there are also many low-level program that does not (bash, pam, etc).