The situation is different with AfferoGPLv3 section 13, where just
using a modified version of the work forces you to convey the
Corresponding Source, from the same server (which could just be from
impractical to impossible, think of a network application running on a
resource-limited embedded system) or from a different server (with all
the already discussed reliability issues, which cause possibly
significant costs).
At the risk of repeating myself, I don't believe this technical challenge of reliably hosting code poses a serious hurdle to compliance with this license.
We have distributed VCS systems available and in widespread use, for example. A GIT/Mercurial/Bazaar/etc setup which is mirrored to multiple servers run by multiple groups would ensure that the source is always available, if the current VCS services pose a problem for AGPLv3 compliance.
I also don't believe the current VCS services have reliability issues to the extent that section 13 compliance is an issue. If a service does go down, it's really not a big hassle to upload the source to another host. In accordance with the AGPLv3 section 8, you have 30 days to do so after being notified of the problem. Does anyone here believe that free VCS services are so fly-by-night that it's reasonable to expect this to happen more than once?
Certainly if they become so, a more reliable free VCS solution could be setup by the community to mitigate future problems.