Well, for me there is nothing unsafe here. If we are happy with two keyword prefixes, maybe dyn struct Trait would be a go: sementically this thing is an ad-hoc struct that wrap a trait object may or may not be a dyn Trait inside.
Would this be necessory? I guess a definition like "dyn struct Trait means the same as dyn Trait if Trait is object safe" would be enough.
This should be a warning, as I proposed.