You can, but there is a big difference: betterC is a subset of D, whereas unsafe Rust is a superset of safe Rust. That is, when you use unsafe, you don't lose any language features. When you drop into betterC, you do lose a bunch of stuff from D.
Those choices for builtin language features date back to the early inspiration from Java, but are increasingly being replaced with library implementations. We've added escape checking to the type system last year, and are currently working on safe aliasing (preventing use-after-free).
So yes, atm. when opting for @nogc you're somewhat at the frontier, and it's mostly a choice if you have time, hard requirements, or am very practised.
Avoiding most (but not all) GC allocations is already widely adopted in D's community though.