Yeah, it should be pretty simple to hide just the text. But if you were to change the layout as well then things could become a bit more complicated - that is if you intend to also make the size of tabs narrow.

To be able to toggle to keep the expanded state you would need to do something more than what can be achieved with css alone. You could for example write an extension that assigned some prefix to window title, and then have extra style rules that would conditionally apply based on that title prefix. It will totally work but you need a custom extension for that.