TensorFlow on HDP will be supported this year. I understood from a conversation with an Hortonworks engineer that running a GPU application like TensorFlow on HDP requires YARN enhancements. They are likely to be included in HDP 3.0, scheduled to be launched at DataWorks conference held in San Jose, June 2018.
If you plan to attend DataWorks in Berlin (April 16-19, 2018), the conference schedule includes 4 presentations and one 2-day workshop in Deep Learning. You may get more updates from that conference and Hortonworks folks attending it.