Firebird 3.0 is officially there and I packaged it for CentOS 7, Mageia and Fedora.
The packages for Mageia are in Mageia repositories for Mageia Cauldron (the version that will become soon Mageia 6). To not break Libre Office that still rely on Firebird 2.5 embeded, I made a separate package for libfbembed2.
The packages for CentOS 7 and Fedora 23 are in my Fedora Copr repository.
I will update it regulary so you could have Firebird 3.0 packages in CentOS 7.
Official Epel for CentOS 7 will stay with Firebird 2.5.
Unfortunately, Firebird 3.0 don't build yet with gcc 6, as you can see in CORE-5099, so no Firebird 3.0 yet for Fedora 24.