I am thinking that many of the options that one has to write in the traditional system Xorg.conf file, have to do with user preferences and thus should not IMHO be set by system administrators. In particular touchpad settings. I currently have several xinput ... lines in my ~/.xinitrc to override defaults. I would like instead that X parses a configuration file of my choosing on startup, which I think would be a better way to set a lot of the per-user configuration. Is what I am asking possible?
Is it possible to have X parse a per-user configuration file?
xorg;not root user
There are options in xorg.conf that it is dangerous to allow ordinary users to set. The X server doesn't know which options or option combinations are dangerous. Therefore there is no general ability for ordinary users to set arbitrary options, by design. Running xinput, xset, xkbcomp and so on from your ~/.xinitrc or other X session initalisation file is the natural way.X.org (like XFree86 before it) provides a limited ability for users to choose between several configuration files that are preset by the system administrator. If you pass the -config argument to the server (e.g. startx -- -config foo) or set the XORGCONFIG environment variable, then the server looks for a configuration file called /etc/X11/$XORGCONFIG (no absolute paths or .. allowed).