I don't have a horse in the race here but guess that a big part would be things like single-character identifiers rather than descriptive names.
A slightly weaker but maybe more realistic example, albeit in mathy terms: pick a language L from the set of all programming languages as your next language, according to a probability distribution of commonality of use in 2020 or so, possibly skewed for your field/interests, and work on it exclusively for 5 years.
If your initial language (before L) was K, you're not terribly likely to have picked a successor language that has any relation to K. If your initial language was C, your successor is likely ALGOL-like, and you probably won't have rewired your brain totally. So coming back to old work after 5 years will likely be less of a shock.
Granted, this is like saying "k is different!", but it ties it to a real-world situation where it could even bother a dedicated k programmer.
I think that's an interesting experiment, but I don't believe it will produce the results you predict: I haven't written in Postscript for over ten years, but I just picked up some random postscript code and have no problem reading it. Why would I expect other programmers to be different in this regard?
However even if it's true for most programmers, why does this definition of "readability" have value?
It's a fair point that you have that ability and hope others will too. They might! I don't know that I would, but I might! I'm pretty stupid sometimes though.
My other comment on the nearby thread likely best-addresses why I think coming back "cold" is useful, based on an assumption that being a novice and being cold are similar, and maybe they're not.
With regard to picking up postscript specifically: I'm not intimately familiar with the language, but the bits I found in a quick search look a) less approachable than javascript to me, so fair point on that, but b) somewhat algol-like. At a glance I felt like I could pick up the flow-of-execution without a lot of work, though I could be wrong.
If it is kind of algol-like, I feel like that plays in favour of my argument a bit -- algol-like languages are so ubiquitous as to be hard to really not use the mental model for 5 years, so we're probably not really coming in "cold" to one.
Postscript is a concatenative (stack-based) language, not algol-like at all. Just as array languages, concatenative ones are terse and regular, but reversed (left-to-right evaluation instead of right-to-left).
A slightly weaker but maybe more realistic example, albeit in mathy terms: pick a language L from the set of all programming languages as your next language, according to a probability distribution of commonality of use in 2020 or so, possibly skewed for your field/interests, and work on it exclusively for 5 years.
If your initial language (before L) was K, you're not terribly likely to have picked a successor language that has any relation to K. If your initial language was C, your successor is likely ALGOL-like, and you probably won't have rewired your brain totally. So coming back to old work after 5 years will likely be less of a shock.
Granted, this is like saying "k is different!", but it ties it to a real-world situation where it could even bother a dedicated k programmer.