3 is the preferred behavior for the moment.
Implementing show-close-button-on-hover via the theme leads to artifacts, as it can cause the label to move around (as showing the close button on the tab makes the contents of the tab more congested, which will push the label out towards the edge). I’d like to add a way to do this where the label doesn’t move around in the future, but until then it’s better not to have the functionality IMO.