Without fresh money to pay off old holders the price cannot continue to rise.
That would have been a pyramid scheme, which bitcoin is absolutely not.
Bitcoin roughly follows Metcalf's law:
"The value of a .... network is proportional to the square of the number of connected users of the system (n2)."
Therefore, to increase in value 1000fold, you only need to increase the number of users about 31.6 fold.
I doubt that there are 30 mil active bitcoin users, but even if there are, 900mil out of 7bil is a possibility (eventually).
I think that someone projected $2-5mil btc with about 400mil active users.