I’m not sure what Melbournians think but from the very little I’ve seen of your news services (for obvious reasons), I’d probably have to say that I’d watch Nine News if I lived down there. I also get the general impression that just as the case is here in Sydney, Nine News has a considerably stronger presenting/reporting team in Melbourne compared to Seven’s.
Correct me if I’m wrong, but isn’t Jen herself approaching retirement age? I don’t think I could predict who’s likely to be the main faces of Seven News Melbourne in a post Mitchell/Keyte-era, probably not good for something which will probably happen within the next 5-10 years or so.
Oh man, that would be an extremely sad news bulletin! 
But when the time comes, I’d imagine that (in no particular order, of course) Tony Jones, Alicia Loxley and Brett McLeod would be the most likely candidates to become Peter Hitchener’s successor.