Mozilla dropping gecko for webkit?
Probably not, because open source developers are traditionally often a bit opinated... But check out this post by AllPeers CTO Matthew Gertner, he thinks there are plenty of reasons to drop gecko for webkit, the biggest one Mozilla's large memory footprint. And of course there are also many drawbacks, most important one is loosing XUL and XPCOM.
All the extensions which helped Firefox to gain momentum, would not be usable anymore at least until a webkit compatible XUL / XPCOM (if that is possible at all) is in place. In this context it is worth to mention that the post comes from an extension developer, so the drawbacks of his proposal would hurt himself as well!