Yes, there are all kinds of wonderful devices we could create a "conceptual design" for, if they could be "powered by an incredibly small, easily rechargeable microbattery."
Therein lies the problem. Solve that one and we'd have electric
cars that go 1,000 miles on a charge. Electric
boats. Utility-scale electric storage
facilities so we can use solar
power at night without maintaining big base-load power plants. The list goes on.