This is a few days late, but I just wanted to let the team know that, as of http://trac.webkit.org/changeset/68166, WebKit can support <a ping> (but support is disabled by default).

The reason I left it disabled by default is that some ports may want to have a mechanism for disabling pings, and I didn't want anyone to accidentally pick it up before they were ready.  I'm happy to flip it to enabled by default if that's what people prefer.

~Nate