[m-ou-se]

Some do. More are active on Reddit. But new proposals can come from anyone. Though, before writing and submitting any, check on the public std-proposals mailinglist if your idea would get any traction. See https://isocpp.org/std/submit-a-proposal

std::set does have a contains() function, it's called count(): http://en.cppreference.com/w/cpp/container/set/count