After futher thought, I'd also like to see Joanna Ampil as Elphaba. Her vibrato can be a bit much at times, although I think she has the chops to pull it off.
not really- kerry ellis is more than capable of doing justice to both roles. She played elzia at drury lane during la cutcheons absence, and shes just spent two years in the queen musical we will rock you, and has refind just the right edge to her voice that elphaba would require, whilst maintaining her classical edge, which would be suitable for glinda.