Over the past few years, rumors have swirled about an Infiniti-badged, four-door version of the Nissan GT-R. Makes sense to us – Infiniti could certainly use a performance halo, and the seemingly forgotten IPL initiative hasn't exactly bore any interesting fruit. Enter the Q50 Eau Rouge, which recently debuted for a second time at the Geneva Motor Show packed with the 3.8-liter, twin-turbocharged heart of Godzilla itself.

Infiniti first showed the Q50 Eau Rouge at the 2014 Detroit Auto Show in January, where it did not have an engine – literally. Nothing was housed beneath its striking red hood. Naturally, this puzzled us, especially considering Infiniti boss Johan de Nysschen's statement that he "insists" the car be put into production.

But as it turns out, the Q50 Eau Rouge wasn't necessarily destined to be the "Infiniti GT-R" we have been hearing about for so long. In fact, several options were explored before the final decision to use the Nissan supercar's engine was even made. So following the Eau Rouge's second coming in Geneva, we talked to Infiniti's senior communications manger, Kyle Bazemore, who shed some interesting light on what almost was.

"We could have chosen other Infiniti engines – the 5.0- and 5.6-liter V8 engines for instance – or one from our Alliance partners," Bazemore told Autoblog. In fact, considering Infiniti parent company Renault-Nissan's partnership with Daimler, it stands to reason that even Mercedes-Benz (read: AMG) could have provided the beating heart for the Eau Rouge.

What's more, Infiniti actually explored alternative-fuel powertrains for use in the Eau Rouge. "Our engineering and product planning teams looked at other solutions, such as versions of our V6 engines, and we even looked at developing a high-power sports diesel, then we narrowed it down according to size, weight, packaging, flexibility and how the powertrain package could be 'Infinitized' for the Q50 experience," Bazemore said. "At one point, we looked at hybrid tuning, where the batteries, electric motor and charging equipment were all uprated to provide significant clean power in the form of an 'electric supercharger.'"

Even then, when the decision came to use the GT-R engine, it wasn't just a plug-and-play exercise.
"It's been mapped to feel like an Infiniti," Bazemore said, "which is to say it feels like a premium sedan engine should, has Infiniti air intakes and swirl pots, and is connected to an Infiniti seven-speed transmission."

Indeed, the version of the GT-R engine used in the Eau Rouge is said to produce 560 horsepower and 443 pound-feet of torque – a gain of 15 hp and a loss of 20 lb-ft versus the Nissan – though it uses the same all-wheel-drive system as the Japanese supercar. Bazemore sums it up, "After everything was considered, the GT-R engine – as a basis with modifications to make it appropriate for an Infiniti – was the clear solution for the Eau Rouge concept car. And ultimately, completely, amazingly fantastical."

Right now, Bazemore tells Autoblog that the Eau Rouge, named after the famous corner at the Circuit de Spa, "provides a glimpse into our vision for high-performance vehicles. It takes the basic design features of the Q50 sports sedan, but combines it with the spirit of Formula One, in which Infiniti is (obviously) involved." In fact, several of the sedan's design elements – specifically the front wing, rear aero packaging and rear foglight – are said to mimic the Red Bull RB9 racecar.

It all looks ready to go, and despite de Nysschen's insistence that the car be green-lit, Bazemore insists that the concept "is just that, a concept for now."

Should the Q50 Eau Rouge get the production nod, pricing will be key. For the model to compete with sport sedans like the Mercedes-Benz C63 AMG or BMW M3, it would likely need to carry a price tag under $75,000. And even if the Eau Rouge were to go up against heavyweights like the Mercedes E63 AMG or BMW M5, base pricing would realistically have to fall between $90,000 and $100,000. But consider that a brand-new 2015 GT-R starts at just under $102,000 – would it make sense for the four-door, presumably more luxurious (and functional) model to retail for less money?

Under the leadership of Carlos Ghosn, the Nissan Group has shown that it's not afraid to break with conventional wisdom and create products that can raise more than a few eyebrows – i.e. the GT-R Juke.

The Q50 Eau Rouge study is also one of those vehicles, and it looks like it may very well be heading towards production, especially after an announcement today, that it has asked four-time F1 world champion and Infiniti brand Director of Performance Sebastian Vettel to begin testing a prototype version of the car.

At the recent Geneva Motor Show, Infiniti confirmed the Q50 Eau Rouge study's Nissan GT-R-sourced twin-turbo 3.8-liter V6 with 568PS (560hp) and 600Nm (592 lb-ft) paired to a full-time, all-wheel drive system with 50/50 front-to-rear torque split and a 7-speed transmission.

Infiniti said that Vettel put the sports sedan through its paces at the Millbrook Proving Ground automotive testing facility in the UK, to evaluate the car's "performance, handling and precision driving".

"Vettel's invaluable feedback will be engineered into the next stages of the prototype's extensive development program – testing components, packaging and viability," said Infiniti, which has not yet reached a final decision on production.

The Japanese carmaker added that it will release further information regarding the Q50 Eau Rouge running prototype on the press day of the 2014 Beijing Auto Show on April 20.