Co-maintainer of Flycheck (an Emacs plugin) here 
Thanks for announcing the change! I think we’ll have to update our syntax checker definition to accommodate it; a regexp description of the new format would be very useful. Alternatively, it would be really nice if rustc/cargo gained the ability to report errors in a more structured format (JSON, or checkstyle, or something that we could parse more reliably than through regexps).
Thanks for all the hard work! The new errors look very nice.