I think Kristin could do a great Defying Gravity... at a Miscast Concert. And how funny would it be to see Idina doing Popular! But seriously switching parts... I don't. Sure, they could both probably pull it off vocally and acting-wise, but neither of them are each others' "types" (although Idina has played ditzy blondes before: Amneris). I'd have to see it to believe it.
No I do not think Kristen could do it...She just would not sound right...her voice is to high and I don't think she would sound right. She's great dont get me wrong but just could not see her being green...she's too....BLONDE!!!
"Even if I could let you see me cry you would never understand what I was feeling inside, you see it and use it but dont believe in it..."
Kristin (with an I) definitley has the technique and training to sing that role, but any trained singer in their right mind wouldnt belt that high, because there are too many risks (nodules, etc.) Personally I'd wanna hear Kristin sing it once, just to hear what it sounds like, but her belt is really bright and might be more offensive to the ear, but i'm all for hearing it.
She wouldn't belt it that high. She could go into a higher mix that would be amazing. Plus, what if she sang the high F as operatic: how could anyone "Bring that down"? Hehe. Plus, if we're going to worry about spelling, Kristin's voice isn't too high for Elphaba. Her range is fine for it (her belting voice can go pretty low). The question is tone color: she's very bright. I don't think Idina could ever play Glinda, and I'd hate to see a switch, but Kristin Elphaba, that might be fun.
I could see Idina playing Glinda if she only had the operatic voice. She has played ditzy drama queens in the past (Amneris, Kate, Maureen). But I could not see Kristin as Elphaba at ALL. As other people have said, their personalities go into it a lot. She seems too bright to sing that, and I just could not imagine her being so intense in NO GOOD DEED and other songs. She's a great belter, but how high can she really go, belting-wise? I think both ladies are perfect in their respective roles.