TBH, there are a lot of hardfork proposals that would give me fewer nightmares than one that implements additional divisibility. It would require that every single piece of Bitcoin software and hardware be updated to handle entirely different magnitudes of amounts and feerates as well as a change in the transaction format because anything more than three more digits of additional precision would no longer fit in a 64-bit integer (which is the current size of the amount field in the output).