Cabot
When NU "renovated" Cabot prior to the 1999-2000 season, the talk was to put a viewing box behind one of the baskets (kind of like they have at Hartford along the sidelines with VIP seating, etc. This would have added a few hundred "luxury" seats and some private boxes. However, when they tore open the guts of Cabot, they had to upgrade all of the wiring, plumbing, etc. from what was code in 1956 to 2000 building code, and that's where the extra cash that was supposed to be spent on the additional seating was used. The cost to put the viewing box, etc behind that one basket is mid to high six figures, and I'm sure if some alum wanted to donate the money, it could be done.
A renovated Cabot was supposed to have 2,500-3,000 seats (at least that's what the blueprint I have says), but once they gutted the buidling the new building codes wouldn't allow them to have bleachers at such a steep angle as they have now (for example, if UNH redid Lundholm or UVM redid Patrick, chances are you wouldn't have such large, steep roll away bleachers as they're not up to most buidling codes). That cost NU about 1,000 seats.
As for putting a second ring around Cabot, I don't think it can be done on the side of the gym behind the benches because that's the outer wall. You conceptually could do it behind the other sideline, but with the angles of seats required, you couldn't do more than 200-300 seats, at a very steep price.
I've always been a proponent of playing games in the Solomon Cage. You could get about 3,500 seats in there, if done properly, but that would cost the indoor track and baseball teams a place to practice.
I was told last night that the actual "seating" in Cabot is 1,450 and there were about 500 standees, to give NU the 2,000 number. The original building certificate was 1,200, then they added the short bleachers under the basket near the visiting team's bench.
NU will play about 4-5 games a year at the Arena starting next year. I know the thoughts are to play BU, UVM, and at least 2 non-conference games at the rink.
The Arena actually is a GREAT place to watch a game if you sit in the first 2-3 rows of the balcony. It is reminiscent of watching a game in the old Boston Garden.