Just published a browser extension that provides EditorConfig support for GitHub.
You can download extension for your browser from the corresponding store:
Extension looks for
.editorconfig file in the root of repository the current file belongs to, and applies it's settings to code viewer and editor. Branch is always taken into account.
In options you can also set default editorconfig that will be used for repos without custom one.
It's built with Kango - cross-browser extension framework.
Code viewer (tabs are set to preconfigured width of 4 instead of GitHub's default 8):
Code editor (preconfigured options are chosen and marked as (auto);
insert_final_newline are taken into account on commit):
Options page (just a default
.editorconfig for repos without custom one):