According to Georg Ortner in one of his streams, there will be no new DTM license for the seasons 2017 or newer.
It will only make sense for 2019 and further...because 2017/18 is basically cosmetics and names. From 2019 on there is basically everything new. Would make a lot more sense to spend the money then. If they do it.
DTM 2018 would mean, they would have to do full Brands Hatch layout and apparently someone at S3S hates it