Just playing catch up on this thread. This is both very exciting and disappointing to me at the same time. I have two girls - 5 and 9 - who both have been playing with my LEGO (and their own newly acquired) of late.
The exciting part of course is a focus on themes that are more traditionally-girl oriented. beauty parlors, vet clinics, etc - I know they will love that. And truth be told, while they enjoy the building aspect, that generally is the means to the end - the play. Once they build a set, they have no desire to ever take it apart again - only to use it in their various role-play activities through use of the minifigures.
The disappointing part however could very well be the incompatibility. They currently have and like many of the city sets. it would be a real shame if the scale on this new line was in-congruent with the city line going forward. I just struggle to understand how LEGO thinks that is a good idea, as mentioned much more eloquently by others above.
The minifigure issue itself is a bit more up in the air for them I think. They currently love the minifigures - and my 5-year old just can't get enough of swapping around different "outfits" on her minifigures all the time. So maintaining a wide variety of hair, clothes, faces, etc is key, moreso probably then minifig versue new fig in and of itself.