In Tron Legacy we have the old man who is good and the younger version who is bad, it is the son who tries to save him and in this it's the daughter.
I did not like the ending of either. It's Sad to know that Elizabeth will never exist now. She was awesome.
As we grow we learn, i have learned that if you don't like me grow up or ignore me.
Uh, spoiler here, but did you play the sequence right after the credits?
In the ending, after the Elizabeths drown you, they start to disappear. It cuts to black right BEFORE the last Elizabeth disappears. You never actually see one of the Elizabeth possibilities being snuffed out.
After the credits, Booker 'wakes up' in his office, in 1893, says something like "Anna, is that you?" and when you open the door to the nursery there's a crib in there. Then it cuts to black.
Now, granted, they don't show the baby in there. But ask yourself, why would Booker have a crib in there if he DIDN'T have a baby?
My guess is that there IS a baby, and Booker raises Elizabeth to adulthood, and something happens that triggers something worthy of an expansion while keeping the Booker/Elizabeth dynamic. This is a version of Elizabeth that was raised by Booker, but still somehow got the power to traverse the multiverse and the last one we DON'T see getting snuffed out.