Re: No boxed gifts please
I've seen it once, and only then.
I understand the concept. But you know what, I still find the request a bit rude. For one thing, I am uncomfortable giving people my age monetary gifts. It feels like a real auntie/uncle thing to do, and it's awkward. So when they make that kind of demand, I don't know what to do.
Anyway, I wouldn't write it.
A bridal registry is fine -- great, in fact!