If using the :target approach, I actually think it's an appropriate use of CSS and HTML. It's not a stretch to consider a tab as a fragment of the document, which can be accessed using the fragment identifier of the URI. After this, hiding the other fragments while showing the target one can also be considered a style choice which is, adequately, achieved via CSS.
Probably people will end up using JS for this, and that's OK, but I really think this approach actually fits the way standards "define" HTML and CSS.
Probably people will end up using JS for this, and that's OK, but I really think this approach actually fits the way standards "define" HTML and CSS.