Realistically, many workers do about 15 hours of actual solid work in a week. It's likely represented as a 10-20 range, but still much closer to ~15 than ~40.

The rest of the time is filler spent on lunches/meetings/communication and 'butts-in-seats' dog and pony show for bad managers.

So I wouldn't say the prediction is that far off-base. Plus we have another 12 years to go.