Yes, people could increase the subdivisibility -- and break a lot of JavaScript implementations in the process.
It's clear that Satoshi either had some affinity to JavaScript or was otherwise familiar with people who are crazy enough to do financial calculations using double-precision floating point numbers, from the fact that the upper limit of existing satoshis is so close to what fits into a double-precision mantissa.
It's clear that Satoshi either had some affinity to JavaScript or was otherwise familiar with people who are crazy enough to do financial calculations using double-precision floating point numbers, from the fact that the upper limit of existing satoshis is so close to what fits into a double-precision mantissa.