I thought about what you said and I made a different calculation.

We have a market cap of $60B and it is estimated that around 5M to 10M unique people are using Bitcoin today. So let's say 7.5M people.
$60B / 7.5M people = $8,000 per person.
$8T / $8,000 = 1B people
So to reach $8T, we would need to expand the Bitcoin community to about 1B unique users. That sounds like a lot, but is it impossible? I don't think so. Facebook was able to build a user base of 2B unique users in a time span of 13 years. (and reached the 1B mark in 12 years) WhatsApp has been able aquire 1B users in 7 years. So it is very much possible for disruptive technologies to experience such an explosion of users.