All it takes is 100% node concensus (e.g. a hard-fork for any non-agree-ers).

Hell, with Entirety-Approval, we could also increase the 20.99999999 limit (it's just a concensus-node rule; all that's needed is agreement).

As the operator of a node for over a decade, now, I do foresee a day when 1 Satoshi [i.e. 0.00000001 BTC] is no longer the smallest divisible unit... one day, perhaps beyond my lifetime, there may be mille- and eventually even nano- Satoshis.

One can continue Dreaming™