Excel::Template is a wacky way to use XML as a templating language. I just use XML::Parser to handle the XML->My Objects layer and write my stuff on top of it. So, E::T is a XML+datastruct->XLS transformer.

In other words, marshalling XML is a solved problem. Don't reinvent that wheel. If you have a cool way to use XML, then build it. Or, publish an RFC here. You'll get a lot of great critique. Maybe, you'll even get someone who says "You know, that sounds very similar to ..." and now you can go ahead and contribute to an existing project. Maybe, just maybe, you might even get someone who says "Wow, that would solve a problem I have. Can I help you?"