I maintained a fork of webkit ~12 years ago and it was a nightmare to maintain because every couple months they would massively reengineer systems and result in

I maintained a fork of webkit ~12 years ago and it was a nightmare to maintain because every couple months they would massively reengineer systems and result in hundreds of non-trivial file changes. And because webkit had a brain-dead way of implementing multi-platform support it meant you spent days or weeks re-integrating these changes.