Editing the z-index of an element via interactions will unlock a range of possibilities. Imagine that you want to click an image and have it expand to fill the screen. If there are any siblings on the page with a competing z-index, there's no easy way to keep them from appearing on top of your expanded element.
A workaround is to create a click-triggered "Show element" interaction pointed at a cloned version of your photo's parent. This cloned parent would have a z-index set higher than any siblings to the page. This ensures no other elements with a higher z-index appear on top of your image as it expands. This is convoluted and gets heavy if your element has many children or any photos.
If Webflow were to allow editing of z-index values directly, it would enable ease of use, peace of mind, and new possibilities (such as the one mentioned above).
Please see attached screenshot and vote on this idea if you agree. And let me know if I am missing an alternative.