As XML is just a syntax it is trivial to convert any LaTeX into XML just by creatimg a file of the form
<latex>... text of latex document with
> replaced by
....</latex> The result is XML but perhaps not what you meant. This isn't just a silly example though, people do such translations to store blobs of TeX in XML databases.
Another conversion to XML can be got by running
latex to get dvi then using
dvisvgm to convert the result to SVG. Again this is XML but perhaps not the kind of XML you intended as it is positioning every character by fixed coordinate positions. It does however cope with a very wide range of TeX inputs.
If you do want to translate to XHTML+MathML, then LaTeXML is a good place to start,