I am happy to announce that an experimental AppImage for the GTK3 version of GIMP is now available for testing.
You can grab the current package from here:
The package will be updated on a weekly basis, like the v2.10.x one.
I am now in the process of checking which plugins are compatible with the GTK3 version , and eventually help updating those that have incompatibilities.
Please report any issue you might encounter, preferentially using the GitHub issues tracker.