No, you can use YQL for any site that you want and even combine multiple queries into a single one. I don’t see any reasons why this project needs to exist…
I haven't read the page, but from the title, I assume it's a scraper
Sure, it can be used for copying data without permission. But not all data is hard to read because they don't want you to copy it. For example, I've built a scraper for a state-run website of company registrations. The data is public, just not in a machine readable format.