The power consumption over the next 50 years is harder to predict than the price. There are many factors simplified above that could change.
You are correct for acknowledging the many known unknowns and potential unknown unknowns, thus I reject this one comment:
So, in order to keep our power consumption under about 2% of world wide power production, we cannot/do not want the price to get to $500,000 before era 6, which is about 2033 or so.
There definitely are physical restrictions with todays technology on the market cap of bitcoin but all of that can change overnight....
Printable solar cells with ASIC's? ASIC space heaters?