[Mathiasdm]

I helped set up such a system for a few hundred developers. We had an 'automated Linus Torvalds', which did the merge, and aborted whenever a file was changed on both sides of the merge.

In the good case (almost every time), there were no conflicts, and the merge went fine (we had unittests, builds and regression tests as extra checks in our CI system).

In the bad case, the developer request was rejected and the developer was told to rebase or merge his code on his own, so the merge issues would be handled.