Right, so it wouldn't really make sense that each team would have one?
I was thinking she could be sort of like the L4D Tank or something, a special event that one team or the other could trigger, and then control in some way.
I guess a 10th class wouldn't be that big of a stretch considering how much the items have already broken up the traditional class dynamics. A 10th class would be interesting, from that video I could see her being a sort of crossover class between Engineer, Spy, and Scout.
What do I know though, I haven't played TF2 in literally years.