I agree that normally their songs are longer live, and once they scale them down for the album they get shorter. But, a 2 ½ hour concert, with 4 new songs (I forgot the one they fused together with Bring the Sun) that took up roughly 2 hours of that time, it's still not far fetched that it would be a double album. Maybe we'll just get fewer songs on it. A song like Frankie M being 45 minutes is almost a CD on its own. Maybe the next album will only be 5-6 songs across 2 discs, but still clocking in at 2 hours. If they were to make it a single disc, they would need to scale down the songs so much, that I don't know if they would feel the same.
Still, 1 cd, 2 cd, 3 cd or 4 cd, the next Swans is at the top of my most excited about list.