Would a Human being, theoretically, be able to function with 80-100 percent brain capabilities unlocked,?

The whole "we only use ten percent of our brains" is a load of BS. It was a myth started by Einstein himself to explain his incredible intellect to us mere mortals. Our brain's neurons are almost always entirely active and firing. If you only used 10% you would probably be in an institution somewhere. So to answer your question, yes we would be able to function with 80-100% unlocked because it already is. There is nothing left to unlock.

I suspect that lots of people on YA are using much less than that :-)

Ignore the urban legend and that movie "Lucy".

You use 100% of your brain, if you didn't, it wouldn't have evolved the way it has. At different times, during different activities, different parts of the brain are in use and others are not, but it all gets used

sounds like youve fallen for the whole "you only use 10% of your brain nonsense"

its bs, we basically use it all.

UPDATE:

thats called a seizure.