I just found out there was a podcast for the Avatar Universe. Dante Basco (Prince / Firelord Zuko) and Janet Varney (Korra) host the show. Since I just found out it existed I am only on episode of 13 as some episodes are an hour long.
Dante & Janet have a tendency to ask their guest which ship they ship. John O'Bryan (Episode 12 27:39 if you'd like to hear it for yourself) is a writer and guest on the show and they posed their shipping question. He is a Zutara shipper and said that "I know we lost that fight". Insinuating that the writers fought for Zutara.
Dante asked were there talks about that (Zutara) in the writer's room? and John answered yeah. Janet said the fact that you were fighting for Zutara was going to rock the internet. It seems like from this interview the writers shipped Zutara but this is one interview alone. It's such a small part of the interview and you may not want to sift through hours of media for these small treasures. I'm going to continue listening and I may update this post if I come across more Zutara related info.
On my end, I'm listening Braving The Elements on Spotify, but I understand there are other options if you'd like to check it out for yourself.
Somewhat of an admission that Kataang was rushed
Somewhat in the same vein, we get a bit of an admission from one of the creators that Kataang was forced. I included the link but if you don't trust the link here's the quote. " Personally, at that point I didn’t want Korra to have to end up with someone at the end of series. We obviously did it in Avatar, but even that felt a bit forced to me. " - Bryan Konietzko.
I added this to this thread because, it begs the question, who wanted Kataang if the writers fought and we have somewhat of an admission of forcing Kataang from half the creators? To be fair his comment may be in retrospect, Kataang felt forced after the series ended and X + years have gone by. Who knows for sure.