It's great research, and very cool design (both mechanically, as well as the driving software), but frankly, these types of flying mechanisms just don't scale well and don't have much use. (But please don't take that of a criticism of their research, I think what they've done is awesome and I really look forward to see what they do next.)
Scaling flapping wing devices up is much easier than making them this small.
e.g. 1 Consider animating falling, scaled at 1 pixel per km vs 1 pixel per meter. The former is much slower.
e.g. 2 An ant can carry several times its own weight, but you can't.
Apparently this was a record-setting duck; we wouldn't want to say "your average human goes 23 mph", even though Usain Bolt has done so.
Please take the 100 mph duck with an appropriate amount of salt (vegetarians, feel free to substitute (the duck, not the salt) with an equal amount of Tofu), and instead read it as 'birds are very fast'.
- Is it that it cannot be miniaturized? However, very small insects seem to use flapping as well.
- Is it this particular mechanical setup that won't scale?
- Is it that vision cannot be miniaturized?
- Is it energy density that is not high enough?
- Is it material strength?
- If the application goal is to for example land in a tree or circumvent all kind of tiny obstacles very fast, are there better mechanisms?
I'm always really interested in miniaturization. From watches to chips. So if someone tells it won't work in a particular field, that's important to know.
I'm sorry, but I'm too lazy to answer all of your questions at the moment, though they're good questions. But generally the answer to all of your questions is "yes." (with the exception of the last question, which is "I don't know", but if you've seen a hummingbird or dragon fly, you know exactly how insanely maneuverable they are, and I don't know if I've ever seen better.
For more information, see: https://en.wikipedia.org/wiki/Ornithopter
All of that being said, there are solar-powered drones with large static wings out there, typically based on glider designs. We can also imagine a design where a drone lands and recharges using solar power for ten minutes, and then flies for a short one-minute trip. With the fly-inspired design in this video, it could probably take off vertically.
One of the reasons these systems (and their insect inspirations) can fly so nimbly, while a jumbo jet or elephant is more plodding in comparison, is the "cube/square law" - an object increases in weight much more quickly than it increases in area, and it in reases in area much more quickly than it increases in length.
You can get a decent ratio of volume (weight and chemical power storage) to surface area and heat dissipation/respiratory potential with tiny systems. If you want a lot of area (solar power insolation), you need to go bigger and slower.