The new Fedora strategy does not say anything about hosting infrastructure.
Please note that I clearly talked only about major Free Software projects. It is reasonable for small projects with limited resources to depend on third-party infrastructure (though Free Software should always be preferred), but projects of the size of Fedora should really be, and are in fact, able to host their own infrastructure. Silverblue by itself is a small project, but it is part of the larger Fedora umbrella and hence should make use of its infrastructure.
For a small project that cannot host its own infrastructure, Free Software should be preferred, so Pagure (even for non-Red-Hat projects) or at least GitLab (though that one is crippleware) would be better places to host them on than the entirely proprietary GitHub. Sometimes, there are technical limitations restricting the possible choices, e.g., I have to host the Kannolo ISOs on SourceForge because they are the only hosting service that accepts 1 GiB ISOs (mirroring them myself is impractical because the bandwidth requirement could grow indefinitely if it becomes popular), but I use a self-hosted Subversion and ViewVC installation (rather than SourceForge’s SCM integration) and Copr (for package building) as the main infrastructure, I use SourceForge only to distribute ISOs.
If these projects are controlled by Red Hat, Red Hat should move them to infrastructure it controls. Canonical is doing that very aggressively, imposing Launchpad for all its projects, a move that also spreads the use of Launchpad (which is sadly proprietary). So why not do the same for Pagure? But of course I have no say whatsoever in Red Hat decisions, I don’t even work for Red Hat.
I think it makes a big difference whether we are talking about moving to a semi-Free solution with a crippleware Community Edition (GitLab) or to an entirely proprietary solution owned by Microsoft (GitHub).