"There is an expectation on the customer's behalf of more and more feature content, more and more safety content - that's always going to be there, that's a fact of life."
Boniface pointed to the lack of success Indian car-maker Tata has experienced with its no-frills Nano, the world's cheapest car.
"I don't think there is any market on earth that has embraced a car like that yet," he said.
"I think it's an admirable pursuit, but the expectation is always going to be for more and more and more.
"There are smart ways to [save weight] and I don't think we are ever going to start de-contenting vehicles."
Ford chief interior designer Mike Arbaugh said customers "want everything" in terms of equipment and interior ambience.
"It's a challenge; you want it to look good, you want it to feel good, you want it to be comfortable, you want the cup-holders, you need the USB ports - it's just a big balancing act," he said.
Arbaugh suggested one feature that could soon be dispensed with is the CD player, because of the number of people using USB music storage or Bluetooth streaming, which would result in a weight saving of more than two kilograms.
He described how the days of saving weight by fitting an instrument panel made from 3.5mm thick hard plastic were over "because nobody liked it", and how engineers have achieved soft-touch vinyl or leather surface finishes without increasing weight.
The underlying substrate was reduced by 1mm and then engineers injected tiny bubbles of nitrogen into the polyurethane.
Chrysler's head of SRT, Viper, Mopar and Motorsports design, Mark Trostle, said the adoption of weight-saving technologies and materials in premium and exotic vehicles will eventually trickle down to mainstream cars.
Trostle said taking more than 45kg out of the new Viper used a lot of materials that are not yet cost-effective, but the company benefited from the project as it allowed for experimentation.
"We are looking at those things in our future products where can we start to use those things on hoods, fenders - where it makes sense," said Trostle.
"Doing supercars or exotic cars is a great way for us to learn as a company as well - there are things that will hopefully trickle through and we can get them into the mainstream world."
Boniface described the weight-saving measure of reducing complexity and the number of components, such as replacing a steel dashboard support that uses several welded brackets with a one-piece tubular magnesium assembly that also serves as the ventilation ducting.
However, Arbaugh suggested customers preferred to be able to see where the car-maker had invested money and said Ford had previously used magnesium for dashboard supports but later decided to spend the money elsewhere.
"That's a lot of money for a very esoteric type material that the customer never sees," said Arbaugh.
Trostle said the continuous reduction in size and weight of some components is helping, using the example of airbags. "Even though there is weight, they [airbags] are getting smaller," said Trostle.
"If you look at the size of a steering wheel airbag and you remember when they first came out - now you would never guess what is packaged in there."
With the larger budgets - and usually size - of premium cars, lightweight construction materials are more viable, but the real challenge is finding cost-effective ways of reducing the weight of mass-market vehicles, on which fuel-saving measures are even more important in terms of corporate average fuel economy (Cafe).
Boniface said on premium vehicles like the Cadillacs, on which he oversees the design, keeping weight down while increasing features was easier.
"It is a little tougher on a Ford or Chevrolet because those are the very vehicles where you need to reduce the mass because there are a lot more of those vehicles [on the road]," said Boniface.
"Yet the price point doesn't allow you to spend money on carbon-fibre, a lot of magnesium castings and so forth."
Boniface said studies undertaken during development of the Chevrolet/Holden Volt showed that 10 counts of aerodynamic improvement (for example from a drag coefficient of 3.1 to 3.0) is equivalent to reducing weight by 22kg.
"Reducing a vehicle's mass by 22kg costs a lot of money," he said. "Aerodynamics in some ways is free, it's testing time and an impact on how the car looks."
However, aerodynamic improvements such as active radiator vents or underbody smoothing have weight implications and can impinge on interior space and visibility.
Arbaugh spoke of the challenges facing an interior designer when aerodynamics dictates the form of a car. "We have to do everything we can to make those pillars look thinner, to keep the vision of the customers," he said.
"It is a challenge to deal with when you have A-pillars creeping in so the air flows around them better, and with safety the pillars are getting thicker. Eventually it all finds itself [encroaching] into the interior, and on the interior you want spaciousness."
