Audi's TT Sportback concept gets 56 mph while putting out 400 horsepower.

Along with the new TTS Roadster unveiled at its Paris Motor Show news conference this week, Audi pulled the wraps off the 400-horsepower TT Sportback Concept.

The four-door version of its little roadster is the latest of three TT show cars the maker has unveiled this year, and Audi CEO Rupert Stadler tells TheDetroitBureau.com, the goal isn’t simply to offer up a few fantasies in chrome. The goal is to gauge public feedback to determine which of the three prototypes should be added to the Audi line-up.

That would become part of a broader expansion of the maker’s product portfolio, Stadler revealing a goal of boosting the current 50 products and variants to 60 by decade’s end.

“At the beginning of the year, we opened up the discussion to see if the TT line could be elaborated,” said Stadler. “Now we are coming to the stage where we to make a decision. The best concept will win.”

At the Paris Motor Show, Audi showed off its updated Audi TT Roadster and TTS.

The shoot-out was set in motion at the 2014 Geneva Motor Show with the unveiling of the 420-horsepower TT Sport Quattro. Drawing heavily from Audi’s racing heritage, it drew upon a 2.0-liter turbocharged four-cylinder engine, delivering power to all four wheels through a beefed-up Quattro drive system. The Sport Quattro was said to be able to launch from 0 to 60 in just 3.7 seconds.

Months later, Beijing Motor Show-goers were treated to a first look at the Audi TT Offroad concept. The four-door prototype didn’t offer quite as much power of the TT Sport Quattro but was far from anemic at 402-hp. That included the 288 ponies punched out by its 2.0-liter turbo gas engine, and 85 kW from an electric motor driving the rear axle. A plug-in hybrid, the package was designed to deliver up to 31 miles in pure electric mode.

(Click Here to check out TheDetroitBureau.com’s complete Paris Motor Show coverage.)

The latest entry, the TT Sportback Concept also goes for a four-door layout that, at 14.7 feet in length, is 11.4 inches longer than the new TT, and 2.4 inches wider, at 6.2 feet. It gains 4.7 inches in wheelbase, at 8.6 feet, but drops about 1.2 inches in height, at 4.5 feet. Making an even 400-hp, the 2.0-liter turbocharged four-cylinder package is said to be able to launch the TT Sportback Concept from 0 to 100 kmh (0 to 62.5 mph) in just 3.9 seconds.

While Stadler and other Audi officials insist they have yet to make a decision about which of the three models they’ll put in production, the CEO might have dropped an inadvertent hint when, in an interview, he noted the luxury brand’s goal of rapidly expanding the number of plug-in models in its line-up. If that’s a key factor, it would appear to favor the TT Sport Quattro shown in Beijing.

(No bull … Lamborghini heats up the horsepower race with 907-hp Asterion concept. Click Here to check it out.)

But, according to Stadler, Audi will first run through the feedback it is getting from potential buyers, while also taking a broader pulse of key markets including Europe, the U.S. and China.

“We have to look for the best opportunity,” added Scott Keogh, head of Audi of America.

(For more on Infiniti’s plans and a preview of a possible new flagship, the Q80 Inspiration, Click Here.)

What’s clear is that whichever new TT variant Audi launches, it will be part of a broader product proliferation strategy that, said Stadler, will see a 20% increase in the brand’s line-up by 2020. By his own count, Audi currently has 50 vehicles and major variants, “and there is potential to go to 60.”

The challenge will be to figure out which are the most lucrative niches – white space, in industry lingo – to fill.

Audi isn’t alone, however. Earlier this year, Mercedes officials announced plans to add 30 all-new or significantly refreshed models by 2020, about one per quarter. BMW has similar plans. Cadillac is rushing to keep up, as is Infiniti, the maker announcing in Paris plans to grow its own portfolio 60% by 2020.