For Fedora 21 there is the KDE Frameworks 5 feature with the goal of shipping all of the KF5 library components that can live side-by-side with KDE4. Some of the packages have already landed into Fedora Rawhide while the rest are expected in the weeks ahead. However, Fedora 21 isn't being released until late in 2014... For Fedora KDE users right now running Fedora 20, fortunately there is a solution.
For Fedora 20 users today there is a Copr repository with KDE Frameworks 5. These KF5 packages have been updated against the 4.99.0 release ahead of their official/stable debut this summer with Plasma Next.
Making things even better for those wanting to experiment with KDE Frameworks 5 packages but without potentially trashing your system, there's a unofficial Fedora 20 Plasma Next ISO spin that contains the new packages atop a Fedora 20 Live base.
More details on the latest KDE work within the Fedora world can be found via Daniel Vrátil's blog.
For non-Fedora KDE users, there are experimental Arch packages available and Project Neon / Kubuntu experimental for Ubuntu users.