Ok, I like this one and I did in the past.
Very conservative back of the envelope calculations.

Let's say Gold is the only Store of Value World Needs Today (not true, conservative).
Gold capitalisation is 7.5 Trillion.
Suppose Bitcoin Matches Gold as Store of Value (conservative, Bitcoin will be  better)
Each one of them would be worth 3.75 Trillions
There will eventually be 21 million Bitcoin  (conservative, 2140 is far in the future)
Each Bitcoin would then be worth roughly 180,000 USD. (conservative, USD is losing value constantly)

So, if you think Bitcoin  (aka Digital Gold) will match (physical) Gold as Store of Value, his terminal value will be 180,000 USD.
47x current valuation.

Hope this isn't getting devoured too early.