I think the ability to add input elements such as checkboxes, radiobuttons, etc. - OUTSIDE of a form - would be very beneficial. The :checked version of these inputs could be used in CSS to create very customizable tab views, like this:
https://codepen.io/mikestreety/pen/yVNNNm

This is related to other requests, such as changing tab orientation, allowing tabs to have a class, and nesting tabs - which I know people have asked for in the past but can't find requests at the moment.

I think this could just be a new module the generates the input element based on a few module attributes. Since it is possible to generate inputs via the "MailForm" module, I would think it would be relatively easy to generate them outside a form??