It's been done before and didn't work out very well. Besides, there are already enough hero wars out there; you can kind a version you like if you look hard enough.
If you are looking for an event, a tournament would still be nice to witness. The only successful one I've seen was a few years ago that FA1 hosted. No one else has ever really put an effort into it, or there was simply too few players.
You could also try to make the grunt position actually worth something more than a peon. It isn't too hard if you have bots. Say that maybe grunts get blank access, while peons only have enough to do shit like ping. That way grunts can boot annoying peons or non-187 people., but still wouldn't be as high as a shaman or chief, of course. You could give grunt access to active/good/cool people. This also helps solve the problem of having tons of people bitching about shaman (if you are experiencing that; most chiefs do). Then again, that isn't really an event, nor a great idea. Eh, whatever.
Maybe we could have Hero Wars: The Musical