Check out the NorthRoadGeo demonstration of the newest features of the upcoming QGIS 3.
There’s also a lot of behind-the-scenes changes which they haven’t touched, e.g. a switch to Python 3 and Qt 5 libraries, a brand new, rewritten QGIS server, new QGIS web client, enhanced metadata integration, GeoNode integration, HiDPI support, a cleaner, stabler, easier PyQGIS API, 1000s more unit tests, and so much more. Get the development from here.
According to this blog QGIS 3 will take some time to launch, maybe a year or so. Since the project timeline cannot be directly ensured because developer force is largely volunteer based or work according to their own companies agendas, all we can do now is to wait and try the latest builds.