Still thinking on this one.....
The original concept had the aircraft operating in a clear space with no need for push backs etc but this does not appear to be an issue.
So........ if the gates were arranged so that the aircraft nosed in towards a central point they would be much closer together there being no terminal building in between.
The advantage of this would be the floor space of the underground terminal building would be much smaller and passengers and crew would have much shorter distances to walk to, from and between gates. Unfortunately that is probably the least likely thing to influence airport designers.