On the flights I have taken of 8+ hours, Hobo Class was simply not available. There might have been some empty middle seats, but I did not see them.
I have not had a successful award upgrade process on a flight over 6 hours in the last two years and I have had to call on one of them to get my money back.
So, while RPUs have worked, I cannot get upgraded to even Hobo Class on long flights.