The change approved at Wednesday's FESCo meeting is around the Format Security feature and involves adding the "-Werror=format-security" compilation flag for all packages in the Fedora repository.
With "-Werror=format-security" set, the GNU Compiler Collection will treat code that's vulnerable to a string format security flaw as a compiler error and fail to build the package. New potential security issues are now prevented from building and entering the Fedora repository, but the upstream code now has to be more careful and ensure they treat handling their strings accordingly.
The Fedora Wiki says there are around 400 packages that will run into problems if this compiler flag is enabled. Yesterday's FESCo meeting minutes notes "AGREED: Give the go-ahead to mass-file bugs (+5,-0,0)" in regards to enabling the "-Werror=format-security" feature of GCC.