tl:dr first:
imagine if bitcoin was: 1bit(100sat)=$1
bitcoin could hold value to $21trillion
which is enough for 4%-8% of the world population
now the waffle to explain
though i dont like to talk about utopian future and dont think bitcoin will become the single "one world currency" everyone uses(because one choice of currency is no choice... and becomes worse than fiat)
there are
2.1 quadrillion units of measure(sats)
as you can see
2,100,000,000,000,000 as sats
21,000,000,000,000.00 as bits
21,000,000.00000000 as bitcoin
so again, having 2 decimals for cents, to have $1 as 100 sats(known as a bit), as i said =$21trillion.
knowing the average savings is $25k. or the amount of combined asset value a person has is $45k average (those people with average value in banks AND assets)
means that if a certain amount of people around the world put everything they have into bitcoin
bitcoin is ok with and would allow for
466,666,666 people assets
or just their savings
840,000,000 people savings
so imagining this growth occurred in a future where the population was ~10bill
bitcoin would be a world currency for 4.6-8.4% of the world population
which is a healthy place to be.
again bitcoin should not become a single "oneworld currency", because that then becomes worse than fiat for many economic reasons. but 4-8% utility is a good healthy amount of population
now with all that said.
i am not saying it will happen over night nor over months/years.. im talking about decades to century.. so dont turn this into a "gigabytes by midnight" FUD debate.
because whats impossible now can b possible in a could decades with natural growth.
just like call of duty HD online gaming was impossible a couple decades ago.. but today is the norm
just like youtube, skype twitch was impossible a couple decades ago.. but today is the norm
So according to your calculation it will be available for 4-8% of population only but the rest of the world is still in the dark side of moon! There should be something different story if we really want bitcoin to be used by each and every person on the earth. May be a government tie up of all the countries (at least those which are friendly nations) this can lead to major change. Just imagine China, India, USA and Europe atlas they have economical relations and they bring this change.
For doing so the limit of bitcoin may be raised to unlimited and the problem of your question (4-8%) may get resolved in no time. The after math would be interesting and worthy I guess.