I see that this has been under consideration for quite some time, but I’d like to bump it to the top and explain my use case. I have a page on one of my sites that contains a lot of important information, but it’s looong. I have partially broken it up by adding an accordion TOC at the top of the page, but it’s still long. I’m envisioning the page laid out with the accordion links pointing to in-page anchors that would display each topic and subtopic (H2, H3) in a tab format. This would shorten it considerably and add visual interest. I also need it to be accessible… keyboard navigation, full Aria for screen readers, etc.
I’ve started coding it myself but am discovering there’s more than initially meets the eye (which is probably part of the reason you haven’t released it yet 
). As far as customization, nothing special, the normal Elfsight degree of user customizing would be fine. Here’s an example UI that would be perfect. It provides color differential between tabs and also elevates the selected tab a bit to visually reinforce it as selected.