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
Bitcoin is not going to be a means of exchange
It is more and more becoming a store of value (sort of "digital gold", as they say). Real physical gold is a lot more expensive in terms of transaction costs (actually, it is a real pain in the ass to move it around in any significant amounts), but does that make it irrelevant or just cheap (not even speaking of killing it)? Not in the least, apparently. So why should Bitcoin be different in this regard? The point to take away from this is, transaction costs are not very important for a store of value. Use altcoins if you need to minimize your transaction costs