> To have GC where it makes sense and doesn't add too much overhead but allowing non-GC objects that require a bit more care and where you know you need to free memory yourself or using some basic smart_ptr-style tracking object?

D is designed exactly like that. In fact, using value types and smart pointers (using `typecons`) is kind of required if you want to keep GC pauses tolerable. On the flipside, a simple GC means no additional overheads like write barriers or remembered sets. Additionally, a borrow checker for D has also been in development (I have not personally checked it out to comment on it though).