I think this interferes too much. An icon indicating that the site is having problems and a second link to a cache would, IMO, be preferable. Such caches in my country are almost certainly copyright infringing if used to redirect users away from the original source - with this modified solution the user chooses. TBH it's probably still strictly a copyright infringement but the situation looks more ethical.
Of course we know that HN won't implement something like this.