the main problems that need solving are how to store enough energy in a light weight form, and inventing stronger, lighter materials.
I agree! But let’s be realistic. It’s only matter of time when this becomes reality. Just not so long ago we were only talking about drones used in military. Today, it’s one of the most used spy planes as well as weapons.
While I'm sure it's becoming possible, that doesn't mean it will be useful in a military sense. We already have tanks. They do not need to be human shaped. By the same token, drones are basically just autonomous airplanes. It would not improve them to make them mimic the shape and movements of a large bird, or dragon, just because it's cool.