Do you have a concrete idea for a new feature for the C++ standard library? [Note: See the last FAQ below for how to propose a core language feature.] Here are some suggestions for how to get started turning it into a proposal.
It may take a few rounds of drafting, but once you see the group start to converge and agree on the need to address this problem and in a concrete proposed design, congratulations! You’ll have got a proposal that’s in shape to be submitted as an official numbered paper for consideration at an ISO C++ standards meeting, where you or a collaborator champion can present it in person for inclusion in the standard.
There is no ISO requirement that something has to be implemented before it's standardized, only that there is consensus on the feature -- but naturally consensus is easier to achieve when there's a working implementation.
Here is how the library subgroups (and then later the full committee) look on questions regarding existing practice: There is a spectrum, where at one end are proposals so simple that they are acceptable without implementation simply based on inspection of the proposal, while at the other end are proposals so worrisome that they are only acceptable after full implementation and widespread use over many years by users with all sorts of different backgrounds running on a wide range of platforms. Where a proposal falls in this spectrum is an individual decision by each committee member.