Also don't forget that code (including the complexity you want to add to it) will probably have only something like an aggragate ~1/3 chance of still being used

Also don't forget that code (including the complexity you want to add to it) will probably have only something like an aggragate ~1/3 chance of still being used in a production scenario 5 years or so away anyway (for any number of reason, product change, feature removal, company bought / sold, the list goes on and on...) of course these numbers are anedotal but the point is it can be detrimental to think your code will run as is for the next million years, especially after the first draft