I get what you're saying about the likelihood of developers having moved on to different projects/companies, but I don't think that issue is specific to this ap

I get what you're saying about the likelihood of developers having moved on to different projects/companies, but I don't think that issue is specific to this approach in any way. Good software should be written on the assumption that someone else is going to be editing your code at a later date anyway. If it's highly readable, then being unable to grab the original developer is less of an issue. This is one of the reasons for the peer code reviews during the original development. I doubt it's really that hard to find developers to work on issues like this. I've always thought the idea that their work impacts millions of people, even though that is a tiny percentage of the total userbase like you said, was one of the big attractions of working at Facebook. If I knew of an issue impacting that many people, I'd be delighted to have solved it.