See some discussion on T4788.
I think part of the confusion around "Edit Blocking Tasks" is because no "Edit Blocked Tasks" action is available. If users had a modal choice between the two, they'd have to think about what they were doing instead of blindly clicking the most-similar link to what they're trying to do, which I suspect may lead to sort of workflow blindness. In particular, I think giving user a modal choice is better than putting them in an "Edit Blocking" mode and requiring them to select "Blocking Tasks", then change them to "Blocked Tasks" using a dropdown (as in T4788#106456), since this is pretty confusing/unintuitive (you have to click an action which is opposite what you actually want to do).
So I'd like to try adding a second action, but this exacerbates the existing problem of all these actions being pretty similar and cluttery. I also expect we'll have more of them in the future (with third-party applications if not other first-party applications). D8685 was one attempt to fix this, but never felt quite right to me. M1464 tackles the clutter problem, but didn't try to address these relationship links.
If we had a good way to fold these, I think it's likely that we could resolve confusion about merging and confusion about blocking tasks by just giving users modal choices so they're forced to pick the one they want.