[pmelendez]

They wouldn't be using the library code. They would just specify what have to be implemented based on the library. They have been doing this with all the libraries that they include in the standard (such as part of boost) and most of the time the resulted specification is way simpler and limited than the original inspiration. Also this is a design for implementation, once done each implementer have to decide how to make it real.

[JasuM]

Boost has a very liberal license, unlike Cairo. C++ libraries, at least the GNU C++ library, have directly based some of their implementations on Boost.

This might lead to C++ library vendors not implementing the standard and requiring using a third party library, perhaps later integrating them into their own libraries.

Thinking about it, it is not probably a bad thing, it will just take longer than with other parts of the standard. Of course, this is just pure speculation and things might turn out very differently.

[pmelendez]

You have a point if implementers choose to use cairo code instead of re-implementer it, but in the other case they don't need to follow any license at all since licenses are valid just for code, unless they have patents on it (which I don't think is the case in libcairo)