During its March 2019 investor presentation AMD has confirmed that the 3000 series Ryzen Threadripper high-end desktop (HEDT) processors and planned to launch before the end of the year. There was so specific date given, but it appears it will be towards the end of the year.
We are expecting 3rd generation Ryzen desktop chips to be available around Computex and since the last 2 generations of Ryzen Threadripper were released in August and October respectively, it seems that 3rd generation Ryzen Threadripper will launch around that time.
Source PCGamesN