A thing GCC does not have
Seriously though, GCC's development plan in terms of when things branch is laid out at http://gcc.gnu.org/develop.html.
Exactly what features will be in the next version of the compiler depends on what is contributed, and when. For this, before every stage1, the Release Manager collects candidate projects in a wiki page and proposes a schedule for the selected projects based on their dependencies. Information about older releases: