In the @rust-lang/lang meeting today, we were saying it'd be a good idea to do a crater run against full NLL just to get a rough idea of how many affected crates there will be.

There are two ways we could do this and both have some value:

• change the "warning lints" to "deny" and then do the crater run. This has the benefit that if crate X fails to compile, dependencies of crate X will still be tested, giving a more accurate overall picture.
• change default borrowck mode to NLL. This has the advantage that some errors (notably regionck errors) that are no longer relevant are disabled. However, I think we will overall get an underestimate this way, plus there are still (maybe) some soundness holes.