[louthy]

> This would enforce bad behaviors and make it even harder for fresh developers to argue against it.

I think this is a significant point. It maintains the status quo. We change our guidance to devs every other year or so. New language features become available, old ones die, etc. But we're not rewriting the entire code-base every time, we know if we hit old code, we refactor with the new guidance; but we don't do it for the sake of it, so there's plenty of code that I wouldn't want in a training set (even if I wrote it myself!)