As of today Plasma 5.8.4, KDE Frameworks 5.29 and KDE Applications 16.12 have become available in our maui-xenial-backports-neon repository.
Plasma 5.8.4 features several bugfixes. Most noticable in the multiscreen handling that should work more reliable. There is a full changelog that you can find here.
KDE Frameworks 5.29 includes some fixes for KIO aswell as some new Icons in the Breeze Icon Theme. See this link to get a full changelog.
KDE Applications 16.12 includes the greatest and latest in terms of Software developed by KDE. This includes a highly improved Kdenlive version with several bugfixes and new features.
Note that this repository is disabled by default and you may decide to activate it either if you want to try out one of the latest versions of Plasma or if you encounter problems with the current version. Please note that after updating, you could also disable the repositories again to stay then on that base.
Read here how to activate backports repositories.