DNF Seems To Be Working Well As Yum's Future Replacement
Since yesterday I've been testing the Fedora 21 alpha release and it's running quite nicely. I've also been trying out the latest release of DNF on Fedora 21 and it's been working out well as a drop-in replacement to Yum.
The DNF next-generation package manager is installed by default on Fedora 21 but it doesn't yet replace Yum. Yum is still present on the system and used as the default package manager. However, with the upcoming Fedora 22 release is where DNF is set to replace Yum. The version found right now on Fedora 21 is DNF 0.6.1 with RPM 4.12.
DNF works just like Yum with all of the same basic commands being supported. In fact, to the casual user, you might not really notice any difference between Yum and DNF.
The only problem I've encountered with my DNF usage on Fedora 21 Alpha has been a problem when setting up the RPM Fusion repository, DNF didn't seem to be able to import the GPG key properly while switching over to using Yum worked just fine.
For those that haven't been following DNF development, it uses the Hawkey library with libsolv as its back-end. Over Yum, DNF is promoted as being faster and simpler while using Hawkey also yields a cleaner API.
On a separate and semi-unrelated note, for the few times when installing RPMs via a GUI, I'm loving the speed of GNOME Software and its application installer on Fedora compared to the sluggish start-up performance of Ubuntu Software Center (at least on Ubuntu 14.04 LTS).