It's completely understandable that some devs don't want to migrate to GTK3 as it just can't be seen as a proper successor of GTK2. GTK3 is still slower, much more unstable and immature than latest (now only maintenance) versions of GTK2. There are many API breaks among minor versions. There are several bugs Red Hat is unwilling to fix. There are several annoyances and anti-features like
mandatory recursive search and several parts of the general widget elements are underdeveloped or intentionally dumbed down to give the unprofessional look of an Android tablet on a desktop computer which is just insane.
I think it would be a better and more constructive idea to consider keeping the latest maintenance release of GTK2 in upstream and maintain it on Debian level with local patches. The only question is whether we have enough maintainers for that.