One satoshi is a very small unit. If bitcoin is worth $100 million, 1 sat would be just $1. Bitcoin price is $16800 presently, but with all-time-high of $69000. That is not close to $100 million at all.
As to why the OP believes we have to hard fork the bitcoin project in order to have smaller units, I don't understand the reasoning behind it. When Bitcoin's price rises up when it crosses one million dollars, then it is still appropriate to use a satoshi as a unit of measurement when talking about bitcoin amounts, and it is important to note that doing a hard fork does not have anything to do with having other bitcoin measuring units because it is simply about placing decimal places rather than doing a hard fork.