zoomrequest event with trackpads?

I'm trying to give pages access to the OS X trackpad pinch gesture event so
that apps can implement custom zooming behavior. Chrome already has this
capability, although they hacked it by sending a normal wheel event with
the control key down instead of creating a new event type (see
https://groups.google.com/a/chromium.org/d/msg/chromium-dev/L_kaBhYFi5U/RIMFBx12dJoJ
for the discussion). The Firefox devs understandably don't want to add this
hack to the web forever, and favor an actual dedicated event (see
https://bugzilla.mozilla.org/show_bug.cgi?id=1052253 for the discussion).

It looks like the zoomrequest IndieUI event could be a good fit (
https://dvcs.w3.org/hg/IndieUI/raw-file/default/src/indie-ui-events.html#zoomrequest).
Is this a good idea? How stable is the IndieUI event spec? Is this meant to
be used with trackpads? It seems like it could be used by translating a
trackpad pinch gesture into a stream of zoomrequest events with a null
originX and originY.