One representative example would be software that is extremely useful to a large group of people but whose packaging is a nightmare. For example, a great many people enjoy the Chromium repository in COPR.

Probably Brackets [1] is a good candidate too. And Atom [2]. Both already are in the COPRs.
[1] http://brackets.io/
[2] https://atom.io/

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Additionally: maybe move all (and/or add new) games to a dedicated COPR could be useful too. Could serve as a testing ground for separation of repos and policies, and as a incentive to have new games packaged for Fedora. The cool thing about this is that it seems like a simple and automatic implementation of the "Rings thing" discussed in another thread.

If above is successful, in a longer term thing: maybe move all the (graphical?) apps to a "Fedora Apps COPR" which uses the libs from the "Official Fedora Repos" to kinda mold and prepare Fedora for the Runtime/Sandbox/Apps future?