What does that guy actually do with the box then? There’s no way his home internet connection could keep it fed. I’m trying to imagine local uses for all that I/O.
The box is for experimentation & learning for fun and profit! :-)
When running some application on the box that processes & reduces the dataset (for example some analytics in RDBMS SQL), then the amount of data returned to the world would be much less than 66 GB/s. I have a 1 Gbit AT&T Fibre at my home(office), so could serve quite a lot through that (until AT&T starts complaining about the "unlimited" bandwidth really not being unlimited after some threshold :-)
But when not hosting stuff in a proper data centre with redundant internet connections, connection reliability would probably be the biggest issue. I've not had that many problems with reliability in the home-office (and occasional online training) usage context, but I'm pretty sure there'd be regular "hiccups" if I tried to serve something with high availability from here :-)