> But I can’t imagine that it’s possible to create a tool that does the reverse: converting Tailwind to semantic HTML and CSS. The only thing you could realistically convert Tailwind to is some other utility framework (e.g., Bootstrap) that locks you in with its own syntax and class names.

I don't understand what is impossible about this. A standard tree walker and a GUI tool to define the individual components will suffice. Or to make things simpler, have a command line tool that takes in the CSS selector/XPath of the desired tag/component and generate the relevant CSS. There are already browser extensions that can do this. Also, nothing is stopping you from writing semantic HTML. Vanilla Tailwind is an (almost) one-to-one bijective mapping to CSS. It does not define your HTML unless you are using prebuilt components.