One of the necessary conditions needed to make cycling popular is safe parking - preferably out of the weather. While bikes require much less space than a car, most cities have problems finding space for large scale bike parking.
This Japanese underground bike park can store 200 bikkes . More details here.
One of the rarest pursuits is the land speed record on a bike. There are various types mostly breaking down to paced, unpaced, and downhill(!). Since work needed to travel fast goes into dealing with air resistance, paced bikes that travel behind a moving wind break are the fastest. They don't have to be aerodynamic but a variety of engineering issues need to be met.
Donhou has made such a beast. Bizarre looking with that huge 104 tooth chain ring, but still a bicycle. Unpaced bikes have to be streamliners. I think the fastest official speed was recorded by Sam Whittingham at just under 83 mph in 2009. Serious aerodynamics and a serious athlete.
Cargo bikes are rare sights in most of the US unless you are in a major bicycling town, but even then there aren't many. In regions where cycling is the norm for a lot of people, they have become accepted ways to move children and almost anything else up to a hundred pounds or so - they are the SUVs of the bike world.
This piece notes about 5,000 are sold in Denmark every year - the equivalent of about 280,000 per year in the US. A very different place.
The trick to improving the efficiency of a car is to reduce its mass and make it more aerodynamic. VW has been working on a vehicle that was once called the 1 liter, but has modified into something that might attract normal buyers ... that is if it was affordable. The XL1 is more of a technology demonstrator that VW is using to learn and gain experience with. Lots of exotic design and materials. Wired has a test.
Edison2 is an attempt at something more practical than the XL1. The Very Light Car is built with inexpensive materials using onventional fabrication techniques.
Moving people towards seriously more efficient vehicles will probably be very difficult unless the costs are much lower than conventional vehicles - something that seems unlikely.
I wouldn't be surprised to see Spirit charge passengers by the pound as they excel at charging for nearly everything else. It might work if they have a large enough pool of potential passengers and might shift their average customer size down cutting costs and potentially allowing for smaller seat pitches and even more seats on a plane. The average traveler might be upset, but a more desirable lighter counterpart may be attracted.