This is actually planned already. Not sure how far along the implementation and progress to stabilization is though.
Edit: Found the RFC: https://rust-lang.github.io/rfcs/2795-format-args-implicit-i... - but I don't see any sign that it has been accepted :-?
Edit II: I had missed the PR and issue at the top :-)
https://play.rust-lang.org/?version=nightly&mode=debug&editi...