Would be happy to try this new unstable version.
You could try building directly from the git tree if you want the absolute latest. However, it's not exactly the easiest thing to do. You need to know how to build from source.
Came across a link recently where it seems like Manjaro has some testing packages with the gtk3 migration code. See here.
Rolling distros should have the latest officially-released packages that are built on GTK3. (Not all components with GTK3 migration code have been officially released yet).