Wow it's been awhile since I last visited this thread! I agree with @CherryBunny, the husband was not changed at last minute - it was just a rumour that's not proven true and based on people's assumption because of the spoiler. Like what I've written above, I truly believe that Taek was planned to be the husband since the start. It was fitting that they had JH narrating the story to throw us off at the beginning....but then his narrating was telling his own story and mistakes when it comes to love. He hesitated too much and that was the message that the writer wanted to deliver to the audience. 

I was on #TeamDS too and it seemed to me that she claimed Taek pretty much from the first episode. She was looking after him, patting his butt and telling him to grow up and marry her something she didn't do with any of the others, not even when she had a crush on them. 

I also think her feelings were pretty clear when she picked the pink mittens even though she had originally really wanted the pink gloves as she told Taek and as JH who was there when she oohed and aahed over them, got for her. Its ironic she didn't pick the gloves JH bought her and he didn't wear the shirt she bought him.