Yesterday I committed a patch to the main OSM mapnik rendering style to render slipways (the icon had been published in the SJJB set, but wasn't in the OSM stylesheet), seemed like an easy fix, so without knowing if there is any protocol to follow I made the change after observing similar commits, and already tile.openstreetmap.org is serving tiles with this slipway icon! Excellent.

There's only one way for progress to occur and that is to get to it and start making those changes happen.