The bicycle itself has been a surprisingly resilient technology: the diamond frame, derailleurs, brake levers, and circular pedal motion have stayed at the core of the concept of the mainstream bicycle for a very long time. Disk brakes came from motorcycles to mountain bikes to road bikes and they may be one thing which might have a bike mechanic from the year 1950 scratching his/her head with a non-e-bike.
Because of the battery on th e-bike, I think a lot of the biggest changes over the next few years will be electronic.
We're already seeing things like blind spot sensors, smart alarms/locks, better lighting systems, smart-watch style monitoring, voice control.
Here are the things I'd like to see
1. better range: this has mostly taken the form of bigger batteries, but I'd actually like to see lighter bikes that are easier to pedal with the motor off (the e-bike version of a hybrid car)
2. I do like the idea of modular batteries (I think Bike Friday has them) instead of bigger batteries. With 3-4 kg batteries, I frequently just need to go a few miles and would rather not carry an extra 10 pounds. Smaller faster chargers are another solution. If there were a way to produce a very small AC charging device that could go to full charge in less than an hour...it almost makes more sense than a battery with a 100 mile range. With my laptop, I find that I generally don't need a 12 hours battery, if I can recharge my 5 hour battery in an hour or so.
3. I would like more creative thinking in marrying the e-bike to cars and public transportation. There's been a lot of activity with folding bikes, but there are things about folding bikes that make them a kind of second best solution. I could imagine marrying the electronic world to the bike rack in various ways or simply making it easier to get the wheels on and off.
I also like the share model for cities and things like one motor married to the share bike might have a lot of potential, though this depends on changes to infrastructure.
Some people have talked about smart highways for cars where cars that get on freeways would give up individual control so that a smart system can run them at higher speeds with the cars running much closer together (6 inches instead of 60 feet). It might be possible to do the same thing with bikes drafting one another, turning a pair or more of e-bikes into a virtual tandem
4. more bad weather riding solutions. My guess is that this will take the form of high tech smart clothing rather than changes to the e-bike itself.
5. if we're going to stick with the diamond frame, I think making the bike seat more comfortable would make a big difference. Again I could see a seat design that adjusts to the way you're moving or the amount of pressure you're putting on the seat, kind of memory foam with an even better memory (or like active noise cancelling headphones, but for butts) or being able to change the position/angle of the seat without having to get off the bike.
6. I'm not a speed guy, but definitely understand how getting the e-bike above 30 mph could make it a more attractive commute option. I personally get nervous at those speeds on a bike, but I think there may be a lot of things that haven't been explored in making a bike safer for higher speed crashes: stabilization, throwing the rider off the bike at a more favorable angle, even better brakes, better warning systems, different protective gear. In the last 45 years, the brakes have gotten better, lights are better, and helmets have gotten more popular, but that's been about it.. Cars changed a lot as they went from 25 mph vehicles to 70 mph vehicles. Bikes need to make similar changes if the e-bike becomes a means to double cruising speed.