So if you had 1 sat before, it now shows as 1.000 sats. "Same amount of money", in the words of Satoshi.
I don't think that's what Satoshi is aiming for, otherwise the Bitcoin supply would not be finite.
So why would we need a hardfork in order to get coins less than one satoshi? Locking mechanisms work perfectly, as we can lock 1 satoshi and get 1000 Msat, as these units can be traded and unlocked when we reach one satoshi.
If Bitcoin development to the point where 1 Satoshi equals 1 USD that means an increase in demand, which means that onChain network will not bear all transactions.
What I'm trying to say is that there will be no hardfork if we reach 1 satoshi = 1 dollar.