The game (and good characters) are all about how the journey changes them. The problem with Joel is that his change has come full circle from a parent > survivor > parent, so there isn't much more wiggle room to explore him. On the other hand, there is plenty of room for the development of Ellie.
One immediate change would obviously be how she would evolve directly after the ending in the encampment. As Joel said, "Don't tell anyone about your ... condition, they'll think you're crazy," and I'm sure Ellie would receive the same advice here too. What would that do to her? Finally, here is a chance for her to be amongst civilised (or close to civilised) human beings but having to keep a secret that could potentially make her a target of either ridicule, fear, expulsion or even attack. That's a lot for a 14 year old head to absorb.
I don't think Ellie could (or would want to) live like that. She would feel like an outsider, an outcast, 'ALONE' and we all know what her greatest fear is. She found solace in nature once before and perhaps she would seek solace there once again, preferring the honesty of survival over the travesty of a secret.
The PS5 Exists.
