Stardock hasn't said what has been updated yet so i've had a quick look at beta2b and here are the changes from 2a that i've noticed.
Poss different Korath pic (looks different to me from memory)
Korath and Kryn movies are back in instead of static image.
New Ship Templates
New DA Manual
Swith Chapter option
Neutral extra tile conquest bug fixed (loaded up old game tried invading and tiles seemed to improve by right amount)
Upgrade Power plants - think this is fixed.
Thats all i've noticed so far i'm sure there are pleny of other changes though.