Taking the ultralight, long-distance hiking paradigm of reducing effort and achieving multi-functionality further, we can arrive at some pretty wacky and unconventional ideas.

Everyone here knows that 15 lbs on your back is a heck of a lot better than 30 lbs on your back. Okay, but how about 15 lbs on a walker or rolling trailer in front or behind you versus 15 lbs on your back. No contest.

What we need is a super-light aluminum-frame back with wheels on the bottom. Whenever the trail becomes smooth, take that puppy off and pull/push it on its wheels. The frame unfolds to become your tarp/tent frame.

Need electrical power for your cell phone or flashlight? The dynamo mechanism puts the brakes on the 'backpack-cart' on downhill sections, saving your knees and storing tons of energy for later use - for instance, powering the heating elements in your special 8 oz blanket that is good down to 40 degrees. If you want, you can even sit on the pack and roll downhill with it, increasing the energy produced by 3-4 times. Why not?

So much potential energy is wasted on endless downhill sections. Surely there must be a way of harnessing some of it!

I could see these kinds of ideas actually catching on in Europe, where so many elderly people do lots of fitness walking on smooth, civilized trails.

What I want is just one layer of clothing that boasts variable/controllable breathability, humidity and warmth! Power for the chip and all will last a whole month per charge -- and the garment will weigh the same as any UL insulation piece -- where the added component weight will be offset by elimination of traditional insulation.

Maybe someday???

I used to carry a SUL pet hamster than ran on a titanium wheel all night. The wheel drove a fan that kept air circulating in the tent and stopped condensation. Electricity was also stored in a battery that powered my coffee maker for a morning brew. The hamster had an allergy to down and he died in his quilt one night after a severe reaction.
I really miss him.
I'm going to make my next hamster a synthetic quilt but have heard that hamsters are not keen on Primaloft. Does anyone know if this is true?
Could there be a market for SUL hamster gear?

Titanium and hamsters are yesterday's news. I use a trio of shrews, trained to run in lockstep. The eat fauna along the trail every 45 minutes, which is a good timer for a 5 minute stop. They produce enough methane to power our stove. Their treadwheel is made of aerogel, impregnated with hydrogen. Their net weight is so low that it doesn't register on a triple beam balance.
The treadwheel drives an E-field generator, much lighter than a classical magnetic generator. Problem is finding enough electrical load to use the capacity generated.

Only real problem is shrews have a short lifespan, so they mate frequently, often interrupting power and methane generation.

I like the idea of the cart.

A few hundred grams of CF or Ti would do as the frame.

4x 20" lightweight bicycle wheels with lightweight road tyres at ~500g each. Add a bit of weight for a pair of sturmy archer dynamo hub/drum brakes, and you may be talking sub 3kg (~6lb) using some cord to pull it along and a single brake cable to control the brakes (or should it be remote control buttons on the top of your trekking poles? There will be plenty of surplus electrical energy).

Rick
There was a cart that could be used as an external frame for a backpack here in Australia a few years ago.( it was made in Europe , Germany (?). The fact that it has disappeared from the market provably shows that it is too much of a niche product.
Niche product=small production run=expensive=too expensive...
Franco

Ditch all the high-tech nonsense and just get helium-filled gear and clothing. As a bonus you can inhale it and entertain your friends with mickey Mouse impersonations.

As far as the cart goes, a lightweight rickshaw-like cart was designed for a Rick Ridgeway, Conrad Anker, Jimmy Chin, and Galen Rowell expedition across Tibet in 2000.
Here's a link to the National Geographic feature.

http://ngm.nationalgeographic.com/ngm/0304/feature6/

They designed it based on a 2 wheeled aluminum frame with mtn. bike tires and a separate set of "balloon" tires for soft ground/mud/sand. Imagine a lightweight rickshaw with hand brakes and a backpack hip belt suspension system to take the load off of your arms. It allowed the party to successfully carry large amounts of food and water.
Looks pretty cool, I've always dreamed of building my own, but when it comes down to it, I just don't really see where I could pull one but the open desert.