This is part of our custom Drupal framework - something every Drupal shop must have to gather all workaround and fixes they put together throuought the years - but could be easily isolated into a module + a core patch (yes core needs to be modified a bit to work with this).
Thanks to this we have boosted performance for our customers without changing a line of code. Indeed, once applied a site builder can set cheap pipe on all blocks and expect awesome performance (we've seen up to x10 on some scenarios) even while trashing page cache, block cache and views cache - not that you wan't to do all that, only when it makes sense. And there is an API for coding big pipe callbacks, so coders can leverage this on other places that are not just blocks.
I might be able to isolate this into a module in a couple of days, but unless it comes out explicitly from a consulting request this won't happen as it is already serving the purpose for all our customers as-is.