Unless the front wheels spin, there are no extra losses, that is the point of faux-wheel-drive systems that are normally 100% FWD (or 100% RWD with front-wheel assist, but better inherent dynamics)
When the rear drivetrain is inactive, when the car is stationary or the rear wheels are rolling the same speed as the front wheels are pulling, the only drawback is vehicle weight. The system is designed for negligible drag losses in normal operation, to preserve MPGs. The tradeoff is that it is in no way pro-active in maintaining traction, and only activates after front traction is already lost.
The rear wheels are not normally engaged, and only engage when viscous fluid heats up due to speed differential between the front transaxle an the rear differential either being still, or playing come-along.
And really, there isn't much reason for Paceman and Countryman not to have a 2.0T. I guess I forgot, or didn't realize that the turbo engine was 1.6 liters, considering how ubiquitous 2.0 liter turbo 4s are becoming... it is like some sort of common confluence that everybody thinks 500ccs per cylinder with 4-cylinders is some sort of magic number now.
At least Evoque has the 2.0T, and a more involved, but similarly laid-out AWD system.