A better pull request like BitBucket is now doing
I just read the article A better pull request by Tim Pettersen from BitBucket.
They implemented another way of diffing in pull/merge requests which will show more information (i.e. potential merge conflicts) before the actual merge takes place. That article also states that GitHub and GitLab does the naïve diff, the inferior one.
So that issue is not a pressing issue, but one that's definitively worth to think about.