>But I do think s-expressions are an improvement over HTML in certain scenarios.

I agree. S expressions are a data interchange format. HTML is a markup language. They solve different problems.

S expressions define nested lists of atoms. HTML describes semantic hypertext documents defined by a document tree made of element nodes as subtrees, attribute nodes as subtree metadata, and text nodes. In some scenarios a uniform data structure like s expressions is nicer to work with.

To be honest it boggles my mind that XML was ever used as a universal data format.