So, in Fedora Workstation 24 we added H264 support through OpenH264. In Fedora Workstation 25 I am happy to tell you all that we are taking another step in improving our codec support by adding support for mp3 playback. I know this has been a big wishlist item for a long time for a lot of people so I am really happy that we are finally in a position to fulfil that wish. You should be able to download the mp3 plugin on day 1 through GNOME Software or through the missing codec installer in various GStreamer applications. For Fedora Workstation 26 I would not be surprised if we decide to ship it on the install media.
Fo the technically inclined out there, our initial enablement is through the mpeg123 library and corresponding GStreamer plugin. The main reason we choose this library over all the others available out there was a combination of using the same license as GStreamer (lgpl v2) and being a well established library used by a lot of different applications already. There might be other mp3 decoders added in the future depending on interest in and effort by the community. So get ready to install Fedora Workstation 25 when its released soon and play some tunes :)
P.S. To be 110% clear we will not be adding encoding support at this time.