SharePoint Server 2019 on-premises will be released mid of 2018

The new Office 2019 will be released mid - 2018.

This release contains

Office Apps  (including Word, Excel, PowerPoint, and Outlook)

Servers (including Exchange, SharePoint, and Skype for Business)

Key SharePoint 2019 features 

• More modern page layouts and site template
• Enhanced support for hybrid environments
• Enhanced support for SPFx, which will become the most important development environment to add functionality to SharePoint
• The modern look will become the default look while the classic look will pushed back
• Out of the box look and feel will get an overhaul, SharePoint 2019 will look modern
• Forms (used in list and libraries) can be edited with PowerApps
• Microsoft Flow will become the default workflow engine, although old workflows will remain usable

• Modern UI
• InfoPath is still supported
•  Improved Sharing capabilities
• Shorter urls
• Share from office
• No Microsoft account needed for sharing securely
• File view analytics
• File previews
• Sync IRM-enabled libraries
• New web parts
• Better Teams and Groups integration
• Mobile App
• Search

if you need further details please refer the Collab365 Community and CMSWire