Not that I expect it but the idea is very intriguing at second thought.

What many people are (reasonably) afraid of at the moment is a de-facto monopoly of Webkit controlled by Google. So that Google is in a position to shape the web for their sole business benefit and against the benefit of the rest of us.

If FF joined the Webkit camp as an active driver, the monopoly (in terms of control) would be mostly gone and be replaced by what I'd call a standard and its broadly spread implementation. A web-standard implementation followed by all major vendors.

Of course branches are likely to divert after a while, but for brief moment in time, everything in web-land would be rainbows and unicorns.