We plan on updating the minimum required version of CMake to 3.13, this will allow simplifying a lot of CMake logic.
It is a good opportunity to update now while we are working toward Slicer 5 which will introduce C++11 features and support for ITKv5.
Ubuntu 18.04 LTS CMake version is too old already (3.10.2 at the time of writing this). Ubuntu 19.04 uses 3.13.4.
Windows and macOS users install CMake from binaries or homebrew, so it is not a problem for those users. Other Linux distros update CMake regularly. For Ubuntu LTS and other linux distribution users, they can download and install from binaries
Work-in-progress PR introducing the changes: 1095
Co-authored by @jcfr