The info above translates to
QUOTEWho cannot away-see now yet over the all-wheel drive lacking, that is here a phosphorus-bright ray of hope shown. As I could draw John Wheeler from the R-S developer, itself Ford Focus and Kuga are so similar under the sheet metal that the complete rear axle of the Allrad SUV could be blocked also in R-S. " Ford Tuner, which are occupied already longer with the mark, should without large problems hinbekommen" , Wheeler explains to me. Even if such a change with 10,000 euros should strike to beech, one would thus receive 305 HP strong Ford Focus R-S with all-wheel drive at the same price as a Evo X and for WRX STi. Equipment might be however still clearly more favorable Ford.
Can't quite make sense of it all but considering Ford have limited the power in the Kuga 2.5T (197bhp, 320Nm) due to drivetrain limitations I wouldn't think using that rear diff/axle set-up would be that practical for taking standard ST horsepower and torque let alone RS type performance.
Being fairly familiar with the underside of my ST I'd be curious as to where a propshaft might fit too.
In an interview about the RS Jost Capito admits Ford tried a 4wd set-up but it wasn't enough fun, I'd hazard a guess that they couldn't get decent enough performance out of the 2.5T motor to overcome the extra weight and transmission losses of 4wd to still provide adequate performance.