With CMake, all the dependencies are listed right there in CMakeLists.txt, so someone creating a port for their OS of choice can damn near copy-paste the dependencies into the file that describes the port in whatever ports/pkg system is in use.
I've never seen CMake be an issue for compatibility across multiple systems, and since it's a ready-made package for basically every OS, build time for CMake should be a non-issue. Even those who build everything from ports wouldn't have much issue because CMake is already used for much of the other infrastructure apps already in use.
