In any case, I'm not sure we actually need more divisibility. Even if 1 BTC = $1M, a satoshi is worth $0.01. Do we really need sub-penny value transactions?
So after all, the conceptual problem of the entire cryptocurrency in general is that people want these transactions in the amount of a penny - the main thing is that it would not be a pure dollar but money in the form of BTC/ETH/whatever that tied to dollar.
You can divide BTC at least as much as you want and let it grow to the most cosmic prices but as long as you yourself tie it to the dollar and do not want to untie it, then you are just hostages of the most hated fiat currency.
That was just a reference to the value of everyday transactions, not a suggestion that anything be "tied" to the dollar. The dollar is the most relevant unit of account today, so it's useful to convey actual value. Much more useful than BTC, which is exponentially rising in price vs. all assets in existence.
All I'm saying is the whole idea of needing sub-satoshi units implies that we will need unrealistically low value transactions in the future, much lower value transactions than exist today. I just don't see the point.