You loose builtin arrays and hashes and need to use a container library instead. Same goes for newing aggegates which can be replaced with smart pointers. Escaping closures (delegates) no longer works, but you can explicitly capture context in a struct.

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.