The whole "cause the dome would crack" thing came only from Winston guys (and it wasnt even quoting him, it was just a "I think he thought the dome would crack etc") and I never believed it one bit because first of all, of all things ripping and breaking on the original it wasnt the dome, secondly, its Cameron. If he wanted something, hed find the way. He comes up with the idea, then he comes up with or creates a new technology or material to realize his designs and vision, not the other way around. But personally I dont like the mutation idea. Maybe it makes sense considering that theyre breeding underneath a "sort of" nuclear reactor, but outside the hands and missing dome (revealing what was essentially underneath the original as well) doesnt seem like mutation thing. I personally prefer the drone-warrior thing or aging explanation