I've heard of this and my conclusion is the same. It takes more energy to power AWD in a vehicle than it does for just a RWD one. You do get better traction but you get a totally different handling vehicle. The weight of the AWD will never go away.
Now, if we apply that to bikes specifically, when the AWD is engaged, you will be powering two wheels across whatever terrain you're trying to do. That isn't bad on pavement or anything light, but you'll feel the burn over rocky uphill climbs and other instances. You give up the handling of a well balanced bike for a different handling bike with different weight distribution. This bike will be heavier than a regular RWD bike because it powers the front too, which will make it slower in straight aways and handle differently on turns. That looks like one neat but complex fork too. I would hate to have to replace that...