Yay, it’s the songdisk evolved! Having some “diff”-like functionality would be very handy, but such a tool should show patterns, instead of XML data.
And since I have this bad habit of saving my songs into so many versions that I sometimes loose track, I actually like this crazy idea. And I happen to have a 200gb hosting account that can host haxx-rns projects.
Although haxx-rns itself isn’t completely functional yet, I think the idea is worth discussing 
Unfortunately, we need a full-fledged Renoise API to achieve this. But until then…