Sounds like a great way to spam and gain link pop without the mods noticing it.
![Smiley](https://bitcointalk.org/Smileys/default/smiley.gif)
Good catch! The HTML is still loaded, even though the text is not shown. Parsers will always read it - humans may not.
Quotes would be a good idea for this, but then some less than honest individuals would modify the quotes.
The best solution is coming - let machine learning insert spoiler tags (or some other name) when the content is duplicated, and draw attention to it when there are modifications.