So if I understand it correctly, this haproxy they suggest is the new central point of failure? Sorry for being skeptical but I'm not really understanding the advantage.
But people would need to know which other domains run the other proxies. Might as well manually type in the other domain.
The only way I see to avoid a SPOF is with anycast, which I think involves running your own ISP to be able to arrange your own BGP sessions and announce at multiple locations.