.pc files miss one of the coolest features of pkg-config, that is, to be able
to track dependencies. To make them provide this information, please add a
proper "Requires:" field to the .pc files shipped by the new modular X.Org.

For example, libSM/sm.pc.in should contain a line like this:
Requires: xproto ice
and similar for most other .pc files throughout the whole X.Org.

(As a maintainer of a distribution now I'm creating packages from X.Org 7.0-rc2,
where (as in most distributions) the libraries are split into two binary
packages: the runtime and the development package. Pkg-config is the only clear
and reliable way to automatically discover the dependencies amongst the -devel
packages in the build system, e.g. to automatically find out that libsm-devel
requires libice-devel and so on. Other methods, e.g. parsing the header files,
.la files or manually maintaining these pieces of information all suck for
various reasons, while with pkg-config this works perfectly (proven by Gnome).
So having the .pc files properly filled out would be a huge help, I hope that
not only for me :-))