Even though Microsoft is putting a lot of engineering and marketing effort in Microsoft Teams, Skype for Business on premises is still heavily used and is not going away any time soon.
So even though Microsoft has not publicly talked about Skype for Business 2019 since Ignite 2017, it may be good to know that Microsoft is still planning to release a new version of Skype for Business Server as part of the Office 2019 release. The only published change since Ignite is that Standard Edition will (luckily) remain: see this MSTechCommunity post.