You can already buy a lot with BTC. BTC could get huge with a price of 40,000$ or more and still be a little bit under the radar.
I don't see that ever happening. 40,000 is a huge number and it just doesn't seem like that could happen. Don't get me wrong I would love it if it did. The dollar will not go away in anyones life time on this board. IT may eventually come to an end but not in our lifetime.