Debian is currently building with GTK 3.8, so it works for them (for now). I don't know when they plan to migrate to 3.10, but it's been out since September so I expect they'll move soonish.
I believe Balint (debian maintainer) monitors ubuntu bugs as well, so you might not have to do anything at all.
Sorry, missed the ubuntu-sponsors subscription.
Debian is currently building with GTK 3.8, so it works for them (for now). I don't know when they plan to migrate to 3.10, but it's been out since September so I expect they'll move soonish.
I believe Balint (debian maintainer) monitors ubuntu bugs as well, so you might not have to do anything at all.