I believe there’s a difference in self custody spending and self custody savings. I don’t think self custody spending will ever be something a non negligible amount of people care about. Many hardcore bitcoiners even take this position. I’ll exclude spending from this thought process.

So I think it’s more of a question about whether or not we can scale bitcoin to a decent chunk of the world (20%?) to a degree that fits their typical behavior of savings/investment transfers. For a financially savvy individual, that would probably just be one transaction a month on average. So for 20% worldwide bitcoin adoption, how many do at least one savings transfer a month today with fiat? 20% of that maybe? Very regional based I’d assume. These are very loose numbers that could be wrong but sounds okay in theory.

So can 4% of the world do one bitcoin transaction a month? I won’t do the math right now. If so, I think it’s in a good spot. If not, maybe some form of covenants can help, especially since they share some idea of eventual settlement under a temporarily shared UTXO.