I wouldn't say it hasn't shown up. The number of ShowHN's per weekend has definitely gone up, and while that isn't rigorous scientific proof, I'd consider is a leading edge indicator of something. Unfortunately, we as an industry have yet to agree on anything approaching a scientific measure of productivity, other than to collectively agree that Lines of Code is universally agree that LoC is terrible. Thus even if someone was able to quantify that, say, they're having days where they generate 5000 LoC when previously they were getting O(500) LoC, that's not something we could agree upon as improved productivity.

So then the question is, lis there anything other than feels to say productive has or has not gone up? What would we accept as actual evidence one way or another? Commits-per-day is similarly not a good measure either. Jira tickets and tshirts sizes? We don't have a good measure, so while ShowHN's per weekend is equally dumb, it's also equally good in the bag of lies, damn lies, and statistics.