The syntax could look familiar to those who write DTDs,

That's one of my objections. this would mainly be of use for people
who have a DTD and would copy the content models from the DTD to the
Xpath,

but with your suggestion the result would be syntactically correct
but mean something completely different to its DTD meaning because of the
namespace issues.

Vim users               donate.
http://iccf-holland.org/donate.html

Web developers           check.
http://www.pinkjuice.com/check/