do you mean the % of humans on the planet, or the % of bitcoin users?

it's impossible for more than 0.295% of the world population to ever have 1 bitcoin, so if bitcoin becomes mainstream, everyone with 1 bitcoin will be the top 0.295% at the least.

but this is assuming 21 million people all have 1 bitcoin, but of course some people have more than 1 bitcon, and many people have less.

so in reality, even less than 0.295% of the world population will have 1 bitcoin. The distribution may be something like this

Top 20% (of world population)
owns about 0.011 (11 millibitcoin) on average. (note that this is the UPPER CLASS)

they have a total of about 15 million bitcoin combined

High 20%
owns an average of 0.0025 bitcoin per person (2.5 millibitcoin)

they have just over 3.5 million bitcoin combined

Middle 20%
average of 0.00075 bitcoin (0.75 millibitcoin)

they have just about a million bitcoin combined (divided over 1.43 billion people!) Note that this is 'middle class'. Having 1 bitcoin would mean you're about 1333 times richer than middle class!

Low 20%
they own just about 200,000 bitcoin combined, each of them having an average of about 0.00015 bitcoin (0.15 millibitcoin)

Bottom 20%

the bottom 1 430 000 000 people will have less than 0.000075 (7500 satoshi) each, their entire 'fortune' is what we now refer to as 'dust'.
The total amount of bitcoin in the bottom 20% of the world will be hardly even 100,000 bitcoin


do you see why many of us think 1 bitcoin would be 1 million+ in value? They are more scarce than you'd think.