This will help us eliminate a lot of cruft in the build system. It's relatively straightforward to get a newer CMake on older Linux distributions, so I don't think this is too onerous on users.
pcmoritz do you anticipate this causing you any issues? On Ubuntu 14.04 you have to get CMake 3.2 from a PPA, the one in mainline is very old. In newer Linuxes I believe it's new enough. You can also obtain cmake from pip and conda