The 6 nm node is scheduled to enter risk production in Q1 2020, almost 1 year after the 5 nm risk production, so the first 6 nm chips will probably ship in mid-2020. The only major benefit brought by the new node is the 18% transistor density increase over the original (non-EUV) 7 nm node and performance will see negligible gains since this is not a full node shrink.
https://www.notebookcheck.net/TSMC-to-introduce-intermediary-6-nm-EUV-based-node.418174.0.html