I'm not really happy about this change, mostly because I remember watching the performances from Plaza Gardens on Sunday nights, and still love that nostalgia when I visit and watch the swing dancers.
Now, about this assertion by so many people that the Plaza/hub is in Main Street: it clearly is not, and never, ever has been.
The point of the hub has always been that this is where all the themed lands come together. Walt Disney hit us over the head with this point over and over. When you stand in the central plaza you can clearly see all the different themes at once. It's the preview for all the experiences you can choose.
This is why I'm getting so tired of reading complaints about Jolly Holiday Bakery, which is on the plaza, not Main Street. Everything is appropriate on the plaza, that's the point. I don't think that a fantasyland themed area at Plaza Gardens would look out of place. In fact, even the tomorrowland entrance is appropriate - it's just that it is ugly. :/
I don't think there are any violations of theme happening here at all; my only qualm is the loss of an iconic landmark (for me, at least) to more princess mediocrity and prepackaged fantasy for girls. I wish they still had the kind of Disneyland that encouraged imagination and creativity rather than complete packages of prewritten scripts for kids.