I can see that. It makes you wonder if there isn't some unfulfilled need here. A place designed specifically for people that want to get work done in a public space. Some coffee shops come close, but better food options with a slightly different atmosphere and seating arrangement. Maybe even lockers to hang your coat, etc.
Both are arbitrary, but I guess I was just coming from the standpoint of just using what is generally used on other large platforms. Makes it a tad less arbitrary (unless the '\' character was pulled from another platform already). At any rate, I think the important thing is not the character mechanism that Hubski uses to initiate a quote, but rather the output of the quote. Currently, it looks like a hyperlink. On say, Reddit, the text is not the color of a hyperlink, and a sidebar is inserted along the body of the quote, clearly identify it as such. Simple and it works. So I guess I really think that weather we use a '>' or a '|' or something else entirely, it doesn't matter. Users will learn the mechanics (though I'm still biased towards using a format in use by another high adoption site). But I think the output is what needs the work. I mean, can we all agree that making a block of text look exactly like a web-standard hyperlink is not optimal? :)