Oh yeah, there's been tons of discussion on this sort of thing. Here's just one example:
My impression based on all of the past chatter I've seen is that unsafe annotations are just not where the big potential wins are right now. What we really need is to keep pushing forward on all the stuff the UCG group is doing, such as pin down an official spec for what is and isn't UB/what unsafe code is "sound" in Rust, but also to what extent soundness/UB-ness can be programmatically checked.