At the WWDC 2018 event in June expect to see Apple announce macOS 10.14. This is the next version of macOS that will come as a free upgrade to many users who are on macOS High Sierra.
This is the same event where we expect to see iOS 12 and we could see many shared features. The biggest rumor is that apps will be able to run on the iPhone, iPad and Mac with macOS 10.14 and iOS 12. This would unify the platform and open up more apps to the mac, but it is just a rumor at this point. Reversible Emoji support could also come to the Mac as part of a new macOS update in 2018.
Expect a developer macOS 10.14 beta as soon as the update is announced and a public macOS 10.14 beta soon after. Count on a full release in September or October.