I haven't heard anything about this, but I really wish it was there by default. I don't think the way it works right now fits anyone's expectations of what the lockfile is supposed to do; the whole point of storing the resolved versions in a file is to, well, lock them, and implicitly updating them every time you build doesn't do that.

As one of the original authors of Cargo, I agree. lockfiles are for apps and CLIs are apps. QED.