The big change needs to happen that shifts away from using expensive materials, although I don't see that happening anytime soon since the most efficient affordable conductor wire is copper, which is expensive, aluminum wire fatigues when flexed and causes failures, and the use of silver or gold for conductors obviously isn't going to get cheaper. Electric motors use pounds of copper windings, and rare earth neodymium or cobalt/ferrous magnets, also not cheap. Batteries, in order to be effective need to use highly reactive rare compounds for strong electrochemical reactions to take place and produce good power for power density on a bike, hence the high cost there.
Then there's the danger involved with high powered electrical systems, and the lack of general knowledge of the public of how to use them safely or service them. 60V and up can kill, high amp flow can burn internal organs, and batteries use caustic electrolyte solutions which can burn or melt skin on exposure. Systems hooked up incorrectly or charged incorrectly can cause shorts which can cause electrical fires and also can cause batteries to explode or burn if discharged rapidly.
Comparing that to the occasional pipe burn or spilled gasoline makes internal combustion engines seem relatively safe. Electrical components and systems must be designed to be completely idiot proof and also tamed down to a level where the average user can work on them and make mistakes with low risk, which means limiting the voltage, current flow, and therefore power output of a bike. That's why most bikes are at 48V or under, because at 60V things can get hairy pretty quick if there is a short or the user neglects to follow safe procedures building or servicing the bike. When they are all worked out well, the systems can be self sufficient and virtually maintenance free, but there are always situations out of the ordinary which can lead to bad things happening, the liability for which manufacturers tend to avoid at all costs.
All of these unavoidable facts about the serious nature of electrochemistry and high powered electrical systems means that it will take a lot of development for these types of things to become widespread, and there will need to be a trained service network for them because the average user of an electric bike is not up to the task of rooting around in its guts or modifying it. All this means money, a whole lot more money than most are willing to pay for a motorized bicycle or moped, when for a couple grand more you can buy an electric car or motorcycle which have established dealer networks.
For most folks looking for pedal assist, keeping it under 1500W and 48V avoids most of the problems, and the associated cost of when you need to upsize everything to make a safe system. Considering how most folks are looking to get more umph from their bikes and want to go as fast as possible, I don't see high powered electrics becoming popular, rather just specialized bikes which can be built or bought for a price commensurate with the components and engineering required to make them work. Maybe if they start mining asteroids and the moon, and rare elements become less valuable than they are today, or better cheaper materials out of common elements are discovered and mass produced, then high technology and high powered electrical devices which meet consumer product guidelines can be made for a reasonable price.
If I had $10K, the choice between a Ducati, Aprilia, GP bike, or a Zero or high powered electric bicycle, I'd probably pick a really nice superbike with nearly 200HP rather than an electric which has novel aspects but fails to meet all criteria for a practical and reliable all around bike, and can be serviced without the risk of getting blown across the room or burnt like corporal punishment if wires cross or you touch it the wrong way.
ful, cooperative friendly world-- i only hope so
