My first impression is that this would be really easy to detect. One look at the source of a page using whitespace steganography and you’ll know something is up. Whereas with images and LSB steganography, unless you’re looking for it with software there aren’t any obvious tells.
There's also the Whitespace programming language:<p><a href="https://en.wikipedia.org/wiki/Whitespace_(programming_language)" rel="nofollow">https://en.wikipedia.org/wiki/Whitespace_(programming_langua...</a>