Attribution by reference to a URL only seems reasonable for online reuse to me. For content added directly to Wikimedia projects, you may be able to get by with including permission to do so in the terms of service, but for 3rd party content that doesn't work. If I write something on another site, release it under CC-BY-SA, and it is them incorporated into a Wikipedia article which is then printed and bound in a book, I expect my name (or pseudonym) to appear in that book. I'm easy going when it comes to the exact details of how it is included in that book, but I expect it to be there. Nothing else seems reasonable to me.