I was afraid this was going to be the next XML manipulation language with a horrible syntax. Howerver, in this project there seems to be a concrete syntax as well.|
Usually people on these kind of XML related languages really don't get the difference between concrete and abstract syntax. I think that XML should be used as a syntax for the abstract syntax of the programming language. In this way you are just exchanging the abstract syntax trees of programs as data between tools. This is exactly the approach of RELAX NG: define a standardized abstract syntax where tools can operate on. There is however also a concrete syntax.
I don't really know this Superx++ project, but looking at the website and the samples, they are doing things already much better: there is a concrete syntax.
If you want a language that helps you in manipulating XML this language doesn't have to use XML syntax. You can easily embed the XML syntax in a more usable concrete syntax for your programming language.