I think there are fundamental technological reasons as well. For example, even if you were willing to never update the OS, could you purchase a 1GB ROM chip for example? If using EEPROM, would the performance match RAM? Most people would not want to trade run time performance for improved boot time.

The thing is, there are far more trade-offs today than there were in the days of the C64. It is a worthwhile goal however, ideally computers should turn on instantly.