We already have milli-satoshis on the lightning network they are charging that as the fees and to get it on the main-chain it would only require a soft fork to add further divisibility

I don't think we need milli satoshis on the base layer, they can be use on lightning and liquid and when you're ready to settle a big amount you can go mainchain

This will make small buys, auto-buys, streaming payments and more so easy and cheap and I think in the future many people won't even touch the base layer