I see your point Peach, but I think it would not turn out great either way.
If the premiere is indeed 2 legs, we will not get to know the cast members as well.
But a 2-hour-long episode with just 1 leg? Hell, I imagine it would seem slow-paced and not help excite the viewers at all.
I think they might do similar introductions as Survivor does - only some people get confessionals to describe themselves at the start of the premiere, then some introductions are stuffed in between the episode and a good portion is just left out, or given the spotlight in the coming episodes.