On systems where I also need to edit files outside my home a lot, I made /.editorconfig a symlink to my homedir's .editorconfig file.

This, however, does not work because of this line in autoload/editorconfig_core/ini.vim:

let l:config_dirname = fnamemodify(a:config_filename, ':p:h') . '/'

The reason is that for /.editorconfig, this produces //.

Changing it to only append the slash if there is none already fixes it:

let l:config_dirname = fnamemodify(a:config_filename, ':p:h:s?/*$?/?')

Not sure if that's the greatest solution, but it definitely is one that works.