If a zip file or tar.gz file is single left clicked in the Files browser, display a list of its contents in the Details pane when the Details pane is visible. If there is a huge list of items, and it takes a while to process, show "Loading ..." in the pane until the list fills out.

This could be a view-only list the same as if you double click on a zip currently, just display it in the Detail pane.