As discussed in the last community meeting we would like to upgrade the minimum mesos compiler version to GCC 4.8+, Clang 3.5. GCC primarily for Linux. Clang for OS X, as well as linux for enabling Mesos tooling improvements (clang-format, clang-tidy among others).
Some documents for reference:
Compilers by Distribution Version
Shows we can get GCC 4.8+ or clang 3.5+ on all supported platforms.