New fan theory
Sedna is 5000 year old May, and Alice is 5000 year old Bubbles.
This actually makes a surprising amount of sense.
I like it as a metaphor, like "All men are sons of Adam". As a literal theory, it's pretty hard to match to the facts.
1. The Blink removed all machines higher-tech than a pump, so how would Alice and Sedna be around if they were machines?
2. The Praesides say that AI isn't possible, and Alice disagrees, but says that any AIs on Earth vanished in the Blink. So Alice and Sedna can't be that. (Unless she's lying)
3. May and Momo don't sleep. But Alice and Sedna do. And they're not just faking it, or they would have noticed Gavia's abduction.
Alice and Sedna show every sign of being from the "enhanced biology" faction of the Pre-Blink society.
But yeah, personality-wise, they do bear a little resemblance to Bubbles and May.
P.S. I think the Praesides are also enhanced biology, as are Ardent and Gavia. There are no AI's left around, except for (I think) the big one that caused the Blink and eliminated all its rivals and creators, to remove competition.