They're going with 3 games in 1 arena and just 1 in the other daily on days with 4 games. And they've seemed to try to pick the least "interesting" games to do that for. The last time they were in Buffalo they used a 2100 seat arena, and the attendance at those games were 1320, 1381, 1400, 1388, 1382, 1400, 1189, 1171, 1108, and 1180. It's not like they sold out and people missed out on going because of a lack of seating. This year there's the added benefit of the 2 arenas literally being side by side, I think you can get from 1 to the other without even going outdoors.
If there's a big influx of fans for the 4 Sweden/Russia v. Belarus/Switzerland games and 1800 seats aren't enough it'll be unfortunate. In reality it'll probably be enough and most fans will be over watching the other group games or the bigger games in pool B.
The biggest issue comes in the 1 QF game that will happen in that arena. They didn't have 4 QF's the last time it was in Buffalo so all playoff games were in he big arena. I assume they'll put the most lopsided non Canada/USA QF game in that arena. So maybe Sweden v. Slovakia/Denmark or Finland v. Switzerland/Belarus if Finland wins the group.
The biggest impact from a not visitor perspective is the 3 games in the 1 arena leads to a different scehdule this year. Instead of the constant overlapping games there will be games at 12, 2, 4 and then when the 4 game finishes it's a little wait until 8 for the final game of the evening.