Maintenance of gconf is somewhat of a seperate thing.
GConf is part of the GNOME 2.x platform, not the 3.x one. Despite that, it is still available + works (builds, etc) + used in 3.x. We already started porting from gconf to gsettings during GNOME 2.x (status at https://live.gnome.org/GnomeGoals/GSettingsMigration). Various bits have been migrated before 3.0 and various after 3.0. The intention was that GNOME 3.0 would only use gconf. Unfortunately that wasn't feasable.
It is not possible is to have one component look at gconf and gsettings/dconf at the same time (for the same setting). That's also really weird to aim for IMO. Whenever possible, settings are migrated from gconf to gsettings/dconf.
GConf even during 2.x hasn't been actively maintained for many years. Even at the time that a lot of programs used it.
For every major release we made promises about what would be supported (API stability for gconf during 2.x). GConf deprecation happened various *years* ago. The result (things being ported) has been pretty gradual.