I don't think there's a clear need for this yet: right now, the code base is still in transition, so we're typemapping a lot of things.

However, in the future, this may change: once we've converted significant portions of the codebase over to Mojo, it may no longer be desirable to maintain C++ mirrors of mojo structs. At that point in time, we'll probably want a way to write validators without actually typemapping.