WordPress might extend the existing template hierarchy in a future version. Your users would get a blank page after an upgrade. So write at least the basic loop, header, footer and pagination.
Another point: I use and see at the index.php
usually as the default template. I treat its layout as the core concept and all other templates as specialized variations. Your theme will be easier to understand if you build a complete index.php
that doesn’t look like a forgotten stepchild.