I think the parent's comment was about using GCC5 to compile all the distro's packages, not just providing GCC5 for its users. The Fedora article is unclear about what they mean, but the consequences they refer to imply using GCC5 to compile their packages.

As far as I know, while your link shows that Debian is getting ready to provide it to its users, they haven't yet formed plans to use it to compile their packages.