One big concern was that there's a lot of pre-existing unsafe code that could rely on the drop being at the end of the scope, and not earlier. And you could imagine where, in a world with early drop, maybe you write some unsafe that's sound, but then the safe code changes, something gets dropped earlier, and now it's not sound anymore.
This doesn't mean that this affects Koka, I haven't spent any time with it yet and so I don't mean to imply this is the wrong decision, just showing some related work.
One big concern was that there's a lot of pre-existing unsafe code that could rely on the drop being at the end of the scope, and not earlier. And you could imagine where, in a world with early drop, maybe you write some unsafe that's sound, but then the safe code changes, something gets dropped earlier, and now it's not sound anymore.
This doesn't mean that this affects Koka, I haven't spent any time with it yet and so I don't mean to imply this is the wrong decision, just showing some related work.