The problem is that it's the 60s. My first thought was "security", but unless you an also teach them about elliptic curves, they're going to use the security of the 1960s, which as we now know isn't very secure.
Maybe at least having security baked in would help make it easier to switch to better security later, like how ssh can use different protocols as old ones are broken. But you'd have to make sure that you were very clever about how it was implemented so that it could be switched without major changes.
Another thought is "more IP addresses", but again you are in the 60s. The computers don't have enough memory to deal with IPv6 length addresses. So again the best you can do is try to set them up with easy upgrades.
Which makes me think the best suggestion would be to teach them about Moore's Law, which of course would have a different name, and try to push for every protocol being extensible as technology grows -- make sure that more octets can be added to IP addresses without them breaking, that security is baked into everything but everything has a way of negating a protocol so that they can be upgraded, that there are no hard upper limits that are assumed and can always be changed.
Basically, teach them what we now know are software best practices -- constants shouldn't be hard coded in the software, they should always be in a separate config.