@manton I’m still not quite sure why it wasn’t a good idea!
1: The only data in the Pingback payload is two URLs. Wrapping this an an XML container that's also doing RPC is incredibly overkill for sending just two values. That's why Webmention went with form-encoded instead, like regular HTML forms, which is about the most compact way you can send two values.
2: Pingback never went far enough with the user experience of displaying them. At best, you'd see a snippet of the text near the link, which it turns out wasn't really that useful or contextual. Once social media started taking off, the interactions there became far richer than seeing the pingback excerpt, so people abandoned them. With Webmention, we're explicitly focusing on enabling the kind of rich interactions people do on social media instead.