Even $100,000 would kill it.  If 1 sat (or even 100 sat) == $1 then the fees would grind the system to a halt.  The fees would be so high relative to the amount sent, that it wouldn't be worth it.  From an investment perspective 1 sat==1$ is a nice round number.  From a users perspective, only being able to buy things divisible by 1$ is crap.