I think you may have found some thing. I've borrowed and put the machine
a old s3 graphics card. After running dpkg-reconfigure xserver-xfree86
and then looking in the log to see i810 still being flagged up it was
clear the dpkg-reconfigure xserver-xfree86 isn't updating the config
file.
I moved XF86Config-4 to XF86Config-4.old and ran dpkg-reconfigure
xserver-xfree86, now looking at the logs I get a different error;
(EE) Unable to locate/open config file
I have looked ing /etc/X11 and there isn't a new XF86Config-4 file.
What do I need to do now to get this file back working under
dpkg-reconfigure xserver-xfree86?