"Having these addresses where we wouldn't even touch half of the bits for decades would have been unpopular with a lot of people, even if he would have been pra

"Having these addresses where we wouldn't even touch half of the bits for decades would have been unpopular with a lot of people, even if he would have been praised for being so forward thinking in the end." Worse perhaps, people, algorithms, hardware, ... will all start to assume those bits are zero and start optimizing for that. We have seen this happen repeatedly throughout history (eg. Lisp pointers would stuff tags in the "spare" bits in addresses, making implementations non-portable). These are all hard problems, but the lesson I take away is to 1. Always have a plan for evolving the design/protocol/API/... 2. Aim for a watertight design that supports 1. (Example: TLS 1.3 puts random stuff into reserved fields so nobody can assume they are zero). 3. Really stretch your imagination about future usages (assume 50+ years) 4. Have a ridiculously comprehensive test suite for both clients and servers It seems clear that in terms of lifetimes, hardware gets used much longer than expected, software even more so (Y2K anyone), but protocols/formats/specs/... literally never dies