It would be nice to switch between different compiler systems based on current requirements. I.e. CLang is known to produce better error messages especially with C++ templates, GCC might be the reference compiler and Icecream supports faster development by reducing compile times.
Since all 3 system produce compatible binary outputs it would be nice to switch without the need to rebuild everything, i.e. dependencies etc. Ideally switch is possible to just run a single build.
Challenge: CMake doesn't support switching compiler for an already configured build system. Normally you would have to delete your build directory and reconfigure or maintain different build directories.