I first asked for this feature on Meta.Christianity.SE. @Flimzy pointed out that this would probably benefit many others, too.
I'd like to see a visually distinct alternate blockquote style. This would be very useful for distinguishing quotes from the Bible and other sources in †.SE. But I'm quite sure there'd be use for it elsewhere, too. I might quote a blog post in one style and API reference in another, or use the feature for easier comparing of two different source texts, intertwined.
>for quoting (or some other additional character:
>> Alternate quote
Have a "hint" not unlike the syntax highlighting language hints used on SO. Something like
<!-- bible -->
> **John 1:1a (ESV)** In the beginning was the Word
...and this would apply a CSS class that changes the background color of the blockquote.