The concept of blocking tasks has received almost no interest since it as added in 2.7. I've also discovered that it's implementation is pretty broken so it doesn't actually block as soon as you have more than 1 cron runner process. The global cron lock which was only required for blocking tasks is was the source of scaling issues.
So I'm proposing to just deprecate this concept completely in 3.9. Does anyone have any valid uses cases for blocking tasks, and is anyone using it in the wild? I've done a bit of a search on github and can't find any 3rd party plugins with tasks using it so far.
See blocking bug:
Proposal to deprecate blocking completely: