In a statement issued today, it reads:
Today, the KDE team updates the 5.11.4 for the maintenance version of the KDE Plasma 5. Plasma 5.11, which was released in October this year, includes a lot of redesigned features and new modules to improve the user's desktop experience. This maintenance version of the update lasted three weeks, including a large number of BUG fixes submitted by KDE contributors. Although the restored BUG is relatively small, it is very important.
KDE Plasma 5.11 will also accept the last maintenance version update, which is scheduled to release Plasma 5.11.5 in January 2, 2018. This also means that the development and maintenance work of this series is coming to an end. The KDE Plasma 5.12 branch will release the Alpha preview in December 21st this year, and the official version will be released in January 30, 2018.