Thomas:
That was the subject of my first article for GOLF Magazine, in 1982. We identified about twenty such holes, and readers submitted a few more.
All of them have been hit in two since then. Many more long holes have been built in the years since, but I don't think there are any that are totally unreachable, if you gave a full field of Tour pros a couple of practice rounds on them.
The most likely way to stop them is to have a huge cross-hazard [aka Hell's Half Acre on #7 at Pine Valley] far enough from the green that it's impossible to reach if you can't get over it ... and make it big enough that it's impossible to get over. So, the cross hazard would have to start +/- 300 yards off the tee, and the hole would have to be 330+ yards from there, with the first 100 yards being water, or sand where you could never expect a good enough lie to try to go for the green.
Is that a great hole? No.