A project

Get the URLs of all 4chan.org textboards (dis.) and scrap and archive them. Use archive.org

The >'s become <span class="quote">, the newlines after the quote become </span>, the [o ] becomes <span class="o">, and [/o ] becomes </span>. The result is

<span class="quote">This <span class="o"></span>
<span class="quote">is how <span class="o"></span>
<span class="quote">you multiline quote, right?</span></span></span>

I think you could also multiline quote with spoilier tags.