As I wrote, I mixed a sort of academic argument with sort of unprovable ponderings - the kind that are fun to muse on but wouldn't really make a paper.

"I fail to see how the potential for change, for the better or otherwise, supports an argument that Darcy is shy."
It doesn't necessarily. I agree with you. I don't want to harp on "shy." I did

"I thought you were suggesting the catalyst for Darcy’s current change in manners and temper was the result of an inner epiphany..." However, I do think Lizzy's reaction was a slap in the face while perhaps not an epiphany of sorts. It certainly wasn't a subtle hint. What is interesting is that he goes about making a change assuming for the most part that he won't be in Lizzy's favor. He does because he respects her opinion and maybe because it's right? For his own sake? My mom always said you have to make a decision because you believe it's right for yourself, not because of someone else's opinion. I believe this speaks well of Darcy and makes him a better person.

This is sort of a bad example of what I mean above, but here it goes. Let's say your marriage stinks and you fall in love with someone else who proproses to you. I don't think you should get a divorce if you wouldn't have otherwise (if the person didn't propose to you). You have to know that you would've gotten a divorce regardless of circumstances for yourself.

I agree that his manifest characteristics of being ill tempered, haughty, proud could very easily remain, but alas he is our hero and Austen puts him in the situations that give him the option to change. Then he changes over time. Seeing him at Pemberley, he is more comfortable and at ease. Perhaps he lets his guard down a bit. From a writer's point of view, it is a tool to allow Lizzy to see Darcy so "en garde" - a "softer" side she hadn't seen when around strangers. It certainly doesn't resolve his actions regarding Jane. Those are hardest to forgive for me as a reader,too.