Hi, just an idea:
I would be interested about sites contacting my sites by trackbacks / pingbacks. I guess this could be monitored by some extra code, similar like blog software offers by default. The collected pings would be forwarded to Piwik. Maybe this information can also be collected via the embedded Piwik-JS code, but I’m not expert enough to talk about the implementation.
This information could be a useful indicator about how much people link to your site from their blogs.