I've played Kasumigaseki, before the changes ... I don't know that it's been opened again yet after the work. Yes, they will do away with the two-green system which was a distraction; they already had done so on their West course.
The East course is one of the most prestigious in Japan -- the club is a bit like Oakland Hills or Winged Foot, with lots of important business people in the membership. It's also prestigious because it "was" one of the only courses where Alison actually was present for some of the work -- Tokyo Golf Club next door was relocated from another location after the war, so it isn't really Alison's. Now, I guess, they've traded that prestige for Olympic prestige.
The rough was not high at all when I played it, but I'm sure they will lean more in that direction for an event, since it is not a long course and I don't think they had too much room to lengthen it. [They had looked at borrowing a couple of holes from the West course to add length, as at Brookline, but I think they decided not to do so.] But, remember, not everyone playing in the Olympics is used to such courses, and I don't think they want to embarrass the bottom half of the field. Mostly, it's a parkland course with relatively small greens and deep green side bunkering, unless Mr. Fazio has changed the green sizes -- he is always wary about making his greens too small.