Absolutely agree. The protocol would be updated. Perhaps by scaling the base unit by 1000 so that there are 2.1 quintillion whole base units instead of 2.1 quadrillion. The protocol won't care what that base unit ends up being called by the ux software, though. IMO, it would make a heck of a lot more sense for ux software to refer to that new base unit by a new name rather than try to redefine an already existing unit of account that currently represents 1/100,000,000 bitcoin.