Ubuntu Developers Working Towards The Eventual Demotion Of GTK2
Not only are Ubuntu developers working towards demoting Python 2 on their Linux distribution but they are also working on being able to demote the GTK2 tool-kit from the main archive to universe followed by its eventual removal in the future.
Matthias Klose is hoping to organize more work towards this slow demotion process of GTK2 and ideally to get some of the issues cleared up ahead of the Ubuntu 18.04 Long-Term Support release in April.
The GTK2 demotion message was just volleyed on ubuntu-devel-announce while this Launchpad search shows some of the bugs as tagged as part of GTK2 demotion.
Among the packages still needing to be updated to GTK3 or otherwise dealt with include the OpenJDK JRE, GParted, various Ibus packages, Graphviz, and others. There are also some notable applications like GIMP that are no longer part of Ubuntu's main archive but also need to be ported to GTK3 (or even GTK4) before GTK2 is eventually removed entirely from Debian/Ubuntu.
Obviously GTK2 will still be available on Ubuntu 18.04 LTS, but hopefully this "demotion" period will motivate more developers to get involved in porting remaining pieces of free software onto GTK3+. This also will mean a better Wayland experience (assuming the apps have no hard X11 dependencies), better performance, etc.