Safari could say "Sorry - <div> tags aren't working in the current release", and all big websites would switch to other html tags in a matter of weeks.
Safari has been very wary of this break-neck speed of how Chrome imposes Google's view of standards onto the world. WebKit team has even walked away from proposals when concerns were not addressed (sadly, I can't find the link in GitHub issues right now. Edit: ).
And yes, lack of manpower is another pressing concern.
"Now I consider this issue as an absolute show stopper. I don't think we want to ever implement this feature in WebKit unless this issue is resolved."