I have a theory, sparked by the physical transformation ability that Queen Chrysalis posses, something it would appear is not only backed up by Luna and Celestia but which seem to be fairly important to their characters, such that a few of the things that they (specifically Nightmare Moon) do wouldn’t even be possible if it weren’t true.
Now, first and foremost, we need to be clear on what exactly it was that Chrysalis (and the Changelings) was doing with her abilities, and what exactly those abilities were.
There seems to be, at least from what I’ve seen, the mistaken belief that it was simple illusion magic, but I believe that it goes far deeper than that, mostly because Chrysalis (and Nightmare Moon, and Celestia) don’t just change their physical appearance, they drastically alter the total space that they occupy.
As evidenced here, the ‘natural’ form that Chrysalis adopts is much larger than the form that Cadance displays. During the time that she masqueraded as the Princess, the Queen of the swarm physically occupied a smaller place in the world, and the bounds of her ‘reaction box’, the points at which she could interact with other beings and objects, changed to suit that. She didn’t just slap a new look across her, she changed herself down to what is, presumably, a molecular level. She doesn’t practice illusion, she practices physical alteration, and the Primary Princesses seem to do the exact same thing.
When dazed, the Changelings appear to revert to a ‘natural’ form, their ‘base form’ as we’ll call it. Now, in the Changeling baseform, they take on a black-carapaced insectoid look, seen here.
When Princess Luna is stunned, she appears to revert to this form:
We do not know, currently, what Queen Chyrsalis’ baseform is, and we haven’t seen Celestia stunned yet, but we do know what they’re capable of turning into (Celestia and Luna, at least) and in Princess Celestia’s case that’s a shining orb of light that resembles her sun, and in Princess Luna’s case it’s a serpentine star-field that seems to slither about most of the second episode of the first season.
Alternatively, if you want to look at it from an entirely different but equally valid angle, those two forms are the Princesses, the core of their beings, the bits of energy to which the rest of their, ultimately false, physical forms anchor themselves. They’re essentially other-worldly creatures of pure power, that generate equine avatars that are capable of being bent to their will (hence Luna’s hair changing, her being able to shift between normal and Nightmare-mode at will) in order to not freak out their subjects.
In either case, I think it’s a very neat thing, and further displays the raw power available at the hooves of the alicorns.
Whether or not Cadance possesses the same capabilities is unknown, but for now I’m presuming that she does not.