http://www.techradar.com/news/office-2019-will-be-windows-10-only

Microsoft has confirmed that Office 2019 will ship in the second half of this year, but when it does become available you’ll need to have a PC running Windows 10 in order to benefit from the next-gen productivity suite.

In a blog post, Microsoft clarified that the new version of Office will only run on Windows 10 (or the next long-time-servicing-channel release of Windows Server).