The rumor is that Ford is working on such a hatch. There's history to the "RS500" name that lends credence to the rumor, without even delving into the specifics of Motor's report. The Sierra Cosworth RS500 was an evolution model (think about the incrementally hotter versions of the E30 BMW M3 and Mercedes-Benz 190E 2.3-16), and its spiritual successor was the last-generation Focus RS500. That was itself a hotter version of the Focus RS.
And Motor acknowledges one truth about the hypothetical new RS500: there's not much power left to be pulled from the 2.3-liter EcoBoost engine. The 2016 Focus RS is running at close to maximum output, so any improvements to acceleration will have to be found with weight reduction. That'll make this RS500 a bit different than its predecessors: more of a lightweight special than a collection of power-adding mods.
Motor's prescription for added performance seems sound. Typical lightweighting tricks, like polycarbonate windows and composite bodywork, could reduce mass significantly. Like the previous Focus RS500, a host of scoops and vents could help with cooling and aero. A front limited-slip differential, as specified in the rumor, seems less likely since the GKN all-wheel-drive system is fairly advanced, but it's still be a possibility. Also less likely but certainly possible is the addition or option of a dual-clutch transmission. The new Focus RS is manual-only, and Ford has already admitted it would consider a dual-clutch if demand warranted, according to Car and Driver.
We'll go one further than Motor and suggest that carbon-fiber wheels would be a great upgrade, provided that Carbon Revolution can make them in a smaller size than the 19 x 11-inch rims fitted to the GT350R. Less unsprung and rotational weight beyond the optional lightweight forged wheels would do wonders. And there's the cool factor. Carbon-fiber wheels are still a big deal, with few automakers offering them from the factory. With GM trying to get in on the game with Carbon Revolution wheels, too, maybe it makes sense for the RS500 to fit 'em as well.
Ford certainly has the resources to at least be playing around with RS500-style mules, getting them ready in case the Focus RS is a runaway hit. Motor is reporting that Ford will watch demand for the Focus RS keenly and make a decision in the future. In the meantime, we'll keep our Nurburgring spies on the lookout for a Ford hatch running around the track in camo with a host of mysterious vents and scoops. Stay tuned.