That's funny, I was at a psy trance party (Halycon) a few weeks ago which took place in the car park on Ewer Street which is very near to the location of Pulse. There were over 1000 people at the event which puts it in superclub league! Very similar feel to the now closed SEOne - ie tunnels under railway tracks, but pretty grungey given that it's still used as a car park! Mind you, the SEOne started life as The Drome, a venue for some pretty big squat parties in the early noughties (The Warp Experience, PLUR, Mindscapes) before it went legit.
The problem with superclub venues like the SEOne is that entry prices are pretty steep and you have to queue for everything (to get in, at the bar, to go out for a smoke, etc). Also they are non smoking venues. I've noticed that since the smoking ban there's been a trend away from trance parties in clubs to parties in squats. At a squat party you can smoke, bar and entry prices are more reasonable, the event can go on longer - well into Sunday in many cases, and security is much friendlier. Ok, the venue may be grotty and toilets pretty disgusting, but these are minor drawbacks for most.
Psy trance squat parties are collaborative efforts with one crew providing the soundsystem, another providing decor, another the bar, nitrous stall, etc. and the most successful parties attract thousands of ppl and have very high production values with excellent sound quality and great decor/visuals. I think this is because - especially in the psy trance scene - ppl put on parties because of their love of the music and it's less about making loads of £££. Squat parties have been in the news recently - due to a techno squat party (Scumoween) in Holborn, and said to cause thousands of £s of damage, but most psy trance squat parties I've been to have been held in more discreet locations in buildings which are scheduled for demolition - eg in Vauxhall where the new American embassy is being built.
In these times of recession and austerity ppl are more reluctant to spend £25 getting in to a club, £4.50 for a can of beer, then have to queue for everything, so now really isn't a good time to be opening a new 4,500 capacity superclub. I give Pulse a year before it folds. Just look what happened to Matter & the SEOne.