> you don't need to fight over it, because it's a local display preference

This has limits.

Files produced with tab=2 and others with tab=8, might have quite different result regarding nesting.

(pain is still on the menu)

Do you mean that files produced with "wide" tabs might have hard newlines embedded more readily in longer lines? Or that maybe people writing with "narrow" tabs might be comfortable writing 6-deep if/else trees that wrap when somebody with their tabs set to wider opens the same file?