Dear god no. I use and love (La)TeX daily to write documents. But as a markup format for data that's supposed to be processed in any way, other than being fed to a TeX engine, it's absolutely terrible. You can't even really parse a TeX document; with all the macros it really is more a program than a document. XML is far from perfect, but it works well as a markup and data exchange format that is well-specified.
Dear god no. I use and love (La)TeX daily to write documents. But as a markup format for data that's supposed to be processed in any way, other than being fed to a TeX engine, it's absolutely terrible. You can't even really parse a TeX document; with all the macros it really is more a program than a document. XML is far from perfect, but it works well as a markup and data exchange format that is well-specified.