[edited out]
Funny I was thinking this earlier in terms of fungibility.
The interest you get from the bank is so they can use your money while you aren't right?
If a service was made to centrally hold bitcoin securely so you don't have to worry, it wouldn't risk the fund at all just cold storage as a promise.
But then, what? no interest?? in fact the opposite, how much will you pay per year for bitcoin fort knox. With guaranteed 1 for 1 you own it coins?
Some percent a year?
Yes, good one, but imagine a situation where you are a middle class guy/gal with a bitcoin stash from 2012 (not me, I bought much later

).
You suddenly got 5, 10, 20 mil $$ in 2021-2025 from your 20 btc that you bought for a couple of hundred $$.
You still got no cash...
The size of your stash would probably cause you to sell a large %%, then try to explain where the immense hoard of $$ come from.
Retain good records, lol.
I don't see how that is a problem. You can easily sell a little bit. You don't have to sell the whole stash. You sell enough to cover your expenses for the next few years... or you sell a little bit at various stages on the way up... Where is the problem, exactly?