It's great news. They could easily have turned it down as a test event and had 10,000 at the game like the Union Grand Final is going to have.
I doubt the crowd would be much higher than that anyway. Cas' allocation is around a quarter of the entire population of the place so I wouldn't expect them to sell any more than 10,000. Saints should sell their allocation by Friday and I imagine Featherstone and York will as well.
It needs to be a sellout though. It'd be embarassing if we couldn't even raise 45,000 for one of only two prestige games we have.