The Debian Release Team has published information on the current development work going into Debian 10 "Buster". The project is about halfway through the development cycle for Buster with a final release expected around the middle of 2019. "In order to minimize the freeze length, we have shortened the transition freeze by one month. In any case, if you are planning a transition, don't leave it until the last moment, or else it may not make it in time for buster. The larger the transition is, the earlier it should happen. We do not have a fixed release date, but given the cadence of previous releases it is likely that the release date will be some time mid 2019." Further information can be found in this mailing list post from the Debian Release Team.