[Gatekeeper]

Pretty sure they've talked about adding more ES ground vehicles at some point, although I'm not certain if they mean buggies or something else. There was also some concept art for a VS vehicle which looked very much like a Thresher and seemed to fit with the current buggy layout (rumble seat, etc.)

It is hard to see what role ES buggies would serve though, I agree. Since the Harasser is super-effective already and has ES weapons - what could a new buggy really add? It's difficult to see how the ES buggies could be any faster, so all that's really left is for them to be slower and stronger, or maybe carry more people.

Honestly though, it seems like they might be better off adding the Deliverer instead - filling the gap between Harassers and Sunderers.