It's cute. I can't deny that. But it got me thinking. Why does everybody assume that the Sirens are a thousand years old and run with it? So, in a fashion not unlike my previous post, here's what we know:
Movie • Banished to the HSAU "ages ago" by Starswirl. • That's all they wrote.
Cartoon • Insect-like ponies. • Regular changelings have single voices -- listen carefully at the giggles when they're breaking the shield. • Can change on a dime. • Cannot instantly tell who's the original and who's a copy in the heat of battle.
Guidebook • Insect features are "designed to scare."
What if the Changelings weren't always as monstrous-looking as they are now?
This is a fairly common headcanon from what I could see, with "they were originally Flutterponies" as a particularly popular specific variant. But I know next to nothing about the Flutterponies, so let's ignore that for a moment.