I've heard this question before and reflected upon it a bit.
For those who don't know, an "Otis" is someone who is willing to give their
land to someone useful when they need someone to take over (or they die). Typically this would be older folks with land who either don't have kids or would rather give their land to people who will maintain it instead of selling it.
You can approach the question from a point of counting up from zero. How many Otises do Paul and I know? Maybe a few dozen. I personally know three locally. Then extrapolate up.
The other way is to take the world population and divide it by 2 million Otises (7.8 billion/2 million = 3,900). So to have "millions" of Otises we need 1 out of every 3,900 humans to be an Otis.
Yes, a lot of people live in poverty or big cities. But keep in mind that an Otis also can just be a financial benefactor. Instead of giving land to a young
PEP participant, they could give start-up coin. Big cities have lots of that sort of Otis.
So based on this squishy math, I think it's very reasonable to say there are millions of Otises out there. To say "tens of millions" would require a little more data collection...