I have never actually come across this before. Then again, I haven't been proactively looking.
I have had a quick look and came across the below quote, in one of John Mueller's Google+ Blog Posts:
AMP, the AMP HTML page must be static as required by the spec, but the
associated web page can be built using JS/PWA techniques. Remember to
use a sitemap file with correct "lastmod" dates for signaling changes
on your website.
In terms of its actual use, I do not see how it would be useful. Following on from @closetnoc's Comment, I feel this is just a case of being fancy for the sake of being fancy. Showing off in other words! :-)
Say you have a user jumping between Tabs, they then look for the Tab they were originally on but it has changed. You would run the risk of the user thinking it was a Pop Up etc and simply close the Tab.
The collective point being ... Don't risk confusing people, or doubting your site's credibility, for the sake of something fancy in the Tab.
I would be interested to see any statistics on this, however. Has anyone implemented this approach and noticed any tangible benefits?