According to reliable sources from both HWX and CDH the new platform will since the merger was sealed with being called Cloudera Data Platform (CDP) a concatenation of (HDP and CDH). Hortonworks will not release a new major version or any version between now and then. The last HDP release is and will remain the 3.x which is being used as the base for integration with the CDH5.
Having said that you should familiarise yourself the 2 versions HDP 3.x and CDH 5 because the knowledge you will acquire will be transportable to the new CDP, I am sure for stability there won't be some new fancy stuff outside these 2 version rumours have it that Ambari will disappear in favor of Cloudera Manager CM but I pray they put sentry to sleep as Ranger is far better and atlas.
Having said that there are too many moving parts to have a final list of components of the new CDP... the Cloudera CEO is gone just too soon ...